xref: /linux/kernel/time/timer.c (revision 3fd6c59042dbba50391e30862beac979491145fe)
1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  *  Kernel internal timers
4  *
5  *  Copyright (C) 1991, 1992  Linus Torvalds
6  *
7  *  1997-01-28  Modified by Finn Arne Gangstad to make timers scale better.
8  *
9  *  1997-09-10  Updated NTP code according to technical memorandum Jan '96
10  *              "A Kernel Model for Precision Timekeeping" by Dave Mills
11  *  1998-12-24  Fixed a xtime SMP race (we need the xtime_lock rw spinlock to
12  *              serialize accesses to xtime/lost_ticks).
13  *                              Copyright (C) 1998  Andrea Arcangeli
14  *  1999-03-10  Improved NTP compatibility by Ulrich Windl
15  *  2002-05-31	Move sys_sysinfo here and make its locking sane, Robert Love
16  *  2000-10-05  Implemented scalable SMP per-CPU timer handling.
17  *                              Copyright (C) 2000, 2001, 2002  Ingo Molnar
18  *              Designed by David S. Miller, Alexey Kuznetsov and Ingo Molnar
19  */
20 
21 #include <linux/kernel_stat.h>
22 #include <linux/export.h>
23 #include <linux/interrupt.h>
24 #include <linux/percpu.h>
25 #include <linux/init.h>
26 #include <linux/mm.h>
27 #include <linux/swap.h>
28 #include <linux/pid_namespace.h>
29 #include <linux/notifier.h>
30 #include <linux/thread_info.h>
31 #include <linux/time.h>
32 #include <linux/jiffies.h>
33 #include <linux/posix-timers.h>
34 #include <linux/cpu.h>
35 #include <linux/syscalls.h>
36 #include <linux/delay.h>
37 #include <linux/tick.h>
38 #include <linux/kallsyms.h>
39 #include <linux/irq_work.h>
40 #include <linux/sched/sysctl.h>
41 #include <linux/sched/nohz.h>
42 #include <linux/sched/debug.h>
43 #include <linux/slab.h>
44 #include <linux/compat.h>
45 #include <linux/random.h>
46 #include <linux/sysctl.h>
47 
48 #include <linux/uaccess.h>
49 #include <asm/unistd.h>
50 #include <asm/div64.h>
51 #include <asm/timex.h>
52 #include <asm/io.h>
53 
54 #include "tick-internal.h"
55 #include "timer_migration.h"
56 
57 #define CREATE_TRACE_POINTS
58 #include <trace/events/timer.h>
59 
60 __visible u64 jiffies_64 __cacheline_aligned_in_smp = INITIAL_JIFFIES;
61 
62 EXPORT_SYMBOL(jiffies_64);
63 
64 /*
65  * The timer wheel has LVL_DEPTH array levels. Each level provides an array of
66  * LVL_SIZE buckets. Each level is driven by its own clock and therefore each
67  * level has a different granularity.
68  *
69  * The level granularity is:		LVL_CLK_DIV ^ level
70  * The level clock frequency is:	HZ / (LVL_CLK_DIV ^ level)
71  *
72  * The array level of a newly armed timer depends on the relative expiry
73  * time. The farther the expiry time is away the higher the array level and
74  * therefore the granularity becomes.
75  *
76  * Contrary to the original timer wheel implementation, which aims for 'exact'
77  * expiry of the timers, this implementation removes the need for recascading
78  * the timers into the lower array levels. The previous 'classic' timer wheel
79  * implementation of the kernel already violated the 'exact' expiry by adding
80  * slack to the expiry time to provide batched expiration. The granularity
81  * levels provide implicit batching.
82  *
83  * This is an optimization of the original timer wheel implementation for the
84  * majority of the timer wheel use cases: timeouts. The vast majority of
85  * timeout timers (networking, disk I/O ...) are canceled before expiry. If
86  * the timeout expires it indicates that normal operation is disturbed, so it
87  * does not matter much whether the timeout comes with a slight delay.
88  *
89  * The only exception to this are networking timers with a small expiry
90  * time. They rely on the granularity. Those fit into the first wheel level,
91  * which has HZ granularity.
92  *
93  * We don't have cascading anymore. timers with a expiry time above the
94  * capacity of the last wheel level are force expired at the maximum timeout
95  * value of the last wheel level. From data sampling we know that the maximum
96  * value observed is 5 days (network connection tracking), so this should not
97  * be an issue.
98  *
99  * The currently chosen array constants values are a good compromise between
100  * array size and granularity.
101  *
102  * This results in the following granularity and range levels:
103  *
104  * HZ 1000 steps
105  * Level Offset  Granularity            Range
106  *  0      0         1 ms                0 ms -         63 ms
107  *  1     64         8 ms               64 ms -        511 ms
108  *  2    128        64 ms              512 ms -       4095 ms (512ms - ~4s)
109  *  3    192       512 ms             4096 ms -      32767 ms (~4s - ~32s)
110  *  4    256      4096 ms (~4s)      32768 ms -     262143 ms (~32s - ~4m)
111  *  5    320     32768 ms (~32s)    262144 ms -    2097151 ms (~4m - ~34m)
112  *  6    384    262144 ms (~4m)    2097152 ms -   16777215 ms (~34m - ~4h)
113  *  7    448   2097152 ms (~34m)  16777216 ms -  134217727 ms (~4h - ~1d)
114  *  8    512  16777216 ms (~4h)  134217728 ms - 1073741822 ms (~1d - ~12d)
115  *
116  * HZ  300
117  * Level Offset  Granularity            Range
118  *  0	   0         3 ms                0 ms -        210 ms
119  *  1	  64        26 ms              213 ms -       1703 ms (213ms - ~1s)
120  *  2	 128       213 ms             1706 ms -      13650 ms (~1s - ~13s)
121  *  3	 192      1706 ms (~1s)      13653 ms -     109223 ms (~13s - ~1m)
122  *  4	 256     13653 ms (~13s)    109226 ms -     873810 ms (~1m - ~14m)
123  *  5	 320    109226 ms (~1m)     873813 ms -    6990503 ms (~14m - ~1h)
124  *  6	 384    873813 ms (~14m)   6990506 ms -   55924050 ms (~1h - ~15h)
125  *  7	 448   6990506 ms (~1h)   55924053 ms -  447392423 ms (~15h - ~5d)
126  *  8    512  55924053 ms (~15h) 447392426 ms - 3579139406 ms (~5d - ~41d)
127  *
128  * HZ  250
129  * Level Offset  Granularity            Range
130  *  0	   0         4 ms                0 ms -        255 ms
131  *  1	  64        32 ms              256 ms -       2047 ms (256ms - ~2s)
132  *  2	 128       256 ms             2048 ms -      16383 ms (~2s - ~16s)
133  *  3	 192      2048 ms (~2s)      16384 ms -     131071 ms (~16s - ~2m)
134  *  4	 256     16384 ms (~16s)    131072 ms -    1048575 ms (~2m - ~17m)
135  *  5	 320    131072 ms (~2m)    1048576 ms -    8388607 ms (~17m - ~2h)
136  *  6	 384   1048576 ms (~17m)   8388608 ms -   67108863 ms (~2h - ~18h)
137  *  7	 448   8388608 ms (~2h)   67108864 ms -  536870911 ms (~18h - ~6d)
138  *  8    512  67108864 ms (~18h) 536870912 ms - 4294967288 ms (~6d - ~49d)
139  *
140  * HZ  100
141  * Level Offset  Granularity            Range
142  *  0	   0         10 ms               0 ms -        630 ms
143  *  1	  64         80 ms             640 ms -       5110 ms (640ms - ~5s)
144  *  2	 128        640 ms            5120 ms -      40950 ms (~5s - ~40s)
145  *  3	 192       5120 ms (~5s)     40960 ms -     327670 ms (~40s - ~5m)
146  *  4	 256      40960 ms (~40s)   327680 ms -    2621430 ms (~5m - ~43m)
147  *  5	 320     327680 ms (~5m)   2621440 ms -   20971510 ms (~43m - ~5h)
148  *  6	 384    2621440 ms (~43m) 20971520 ms -  167772150 ms (~5h - ~1d)
149  *  7	 448   20971520 ms (~5h) 167772160 ms - 1342177270 ms (~1d - ~15d)
150  */
151 
152 /* Clock divisor for the next level */
153 #define LVL_CLK_SHIFT	3
154 #define LVL_CLK_DIV	(1UL << LVL_CLK_SHIFT)
155 #define LVL_CLK_MASK	(LVL_CLK_DIV - 1)
156 #define LVL_SHIFT(n)	((n) * LVL_CLK_SHIFT)
157 #define LVL_GRAN(n)	(1UL << LVL_SHIFT(n))
158 
159 /*
160  * The time start value for each level to select the bucket at enqueue
161  * time. We start from the last possible delta of the previous level
162  * so that we can later add an extra LVL_GRAN(n) to n (see calc_index()).
163  */
164 #define LVL_START(n)	((LVL_SIZE - 1) << (((n) - 1) * LVL_CLK_SHIFT))
165 
166 /* Size of each clock level */
167 #define LVL_BITS	6
168 #define LVL_SIZE	(1UL << LVL_BITS)
169 #define LVL_MASK	(LVL_SIZE - 1)
170 #define LVL_OFFS(n)	((n) * LVL_SIZE)
171 
172 /* Level depth */
173 #if HZ > 100
174 # define LVL_DEPTH	9
175 # else
176 # define LVL_DEPTH	8
177 #endif
178 
179 /* The cutoff (max. capacity of the wheel) */
180 #define WHEEL_TIMEOUT_CUTOFF	(LVL_START(LVL_DEPTH))
181 #define WHEEL_TIMEOUT_MAX	(WHEEL_TIMEOUT_CUTOFF - LVL_GRAN(LVL_DEPTH - 1))
182 
183 /*
184  * The resulting wheel size. If NOHZ is configured we allocate two
185  * wheels so we have a separate storage for the deferrable timers.
186  */
187 #define WHEEL_SIZE	(LVL_SIZE * LVL_DEPTH)
188 
189 #ifdef CONFIG_NO_HZ_COMMON
190 /*
191  * If multiple bases need to be locked, use the base ordering for lock
192  * nesting, i.e. lowest number first.
193  */
194 # define NR_BASES	3
195 # define BASE_LOCAL	0
196 # define BASE_GLOBAL	1
197 # define BASE_DEF	2
198 #else
199 # define NR_BASES	1
200 # define BASE_LOCAL	0
201 # define BASE_GLOBAL	0
202 # define BASE_DEF	0
203 #endif
204 
205 /**
206  * struct timer_base - Per CPU timer base (number of base depends on config)
207  * @lock:		Lock protecting the timer_base
208  * @running_timer:	When expiring timers, the lock is dropped. To make
209  *			sure not to race against deleting/modifying a
210  *			currently running timer, the pointer is set to the
211  *			timer, which expires at the moment. If no timer is
212  *			running, the pointer is NULL.
213  * @expiry_lock:	PREEMPT_RT only: Lock is taken in softirq around
214  *			timer expiry callback execution and when trying to
215  *			delete a running timer and it wasn't successful in
216  *			the first glance. It prevents priority inversion
217  *			when callback was preempted on a remote CPU and a
218  *			caller tries to delete the running timer. It also
219  *			prevents a life lock, when the task which tries to
220  *			delete a timer preempted the softirq thread which
221  *			is running the timer callback function.
222  * @timer_waiters:	PREEMPT_RT only: Tells, if there is a waiter
223  *			waiting for the end of the timer callback function
224  *			execution.
225  * @clk:		clock of the timer base; is updated before enqueue
226  *			of a timer; during expiry, it is 1 offset ahead of
227  *			jiffies to avoid endless requeuing to current
228  *			jiffies
229  * @next_expiry:	expiry value of the first timer; it is updated when
230  *			finding the next timer and during enqueue; the
231  *			value is not valid, when next_expiry_recalc is set
232  * @cpu:		Number of CPU the timer base belongs to
233  * @next_expiry_recalc: States, whether a recalculation of next_expiry is
234  *			required. Value is set true, when a timer was
235  *			deleted.
236  * @is_idle:		Is set, when timer_base is idle. It is triggered by NOHZ
237  *			code. This state is only used in standard
238  *			base. Deferrable timers, which are enqueued remotely
239  *			never wake up an idle CPU. So no matter of supporting it
240  *			for this base.
241  * @timers_pending:	Is set, when a timer is pending in the base. It is only
242  *			reliable when next_expiry_recalc is not set.
243  * @pending_map:	bitmap of the timer wheel; each bit reflects a
244  *			bucket of the wheel. When a bit is set, at least a
245  *			single timer is enqueued in the related bucket.
246  * @vectors:		Array of lists; Each array member reflects a bucket
247  *			of the timer wheel. The list contains all timers
248  *			which are enqueued into a specific bucket.
249  */
250 struct timer_base {
251 	raw_spinlock_t		lock;
252 	struct timer_list	*running_timer;
253 #ifdef CONFIG_PREEMPT_RT
254 	spinlock_t		expiry_lock;
255 	atomic_t		timer_waiters;
256 #endif
257 	unsigned long		clk;
258 	unsigned long		next_expiry;
259 	unsigned int		cpu;
260 	bool			next_expiry_recalc;
261 	bool			is_idle;
262 	bool			timers_pending;
263 	DECLARE_BITMAP(pending_map, WHEEL_SIZE);
264 	struct hlist_head	vectors[WHEEL_SIZE];
265 } ____cacheline_aligned;
266 
267 static DEFINE_PER_CPU(struct timer_base, timer_bases[NR_BASES]);
268 
269 #ifdef CONFIG_NO_HZ_COMMON
270 
271 static DEFINE_STATIC_KEY_FALSE(timers_nohz_active);
272 static DEFINE_MUTEX(timer_keys_mutex);
273 
274 static void timer_update_keys(struct work_struct *work);
275 static DECLARE_WORK(timer_update_work, timer_update_keys);
276 
277 #ifdef CONFIG_SMP
278 static unsigned int sysctl_timer_migration = 1;
279 
280 DEFINE_STATIC_KEY_FALSE(timers_migration_enabled);
281 
timers_update_migration(void)282 static void timers_update_migration(void)
283 {
284 	if (sysctl_timer_migration && tick_nohz_active)
285 		static_branch_enable(&timers_migration_enabled);
286 	else
287 		static_branch_disable(&timers_migration_enabled);
288 }
289 
290 #ifdef CONFIG_SYSCTL
timer_migration_handler(const struct ctl_table * table,int write,void * buffer,size_t * lenp,loff_t * ppos)291 static int timer_migration_handler(const struct ctl_table *table, int write,
292 			    void *buffer, size_t *lenp, loff_t *ppos)
293 {
294 	int ret;
295 
296 	mutex_lock(&timer_keys_mutex);
297 	ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
298 	if (!ret && write)
299 		timers_update_migration();
300 	mutex_unlock(&timer_keys_mutex);
301 	return ret;
302 }
303 
304 static struct ctl_table timer_sysctl[] = {
305 	{
306 		.procname	= "timer_migration",
307 		.data		= &sysctl_timer_migration,
308 		.maxlen		= sizeof(unsigned int),
309 		.mode		= 0644,
310 		.proc_handler	= timer_migration_handler,
311 		.extra1		= SYSCTL_ZERO,
312 		.extra2		= SYSCTL_ONE,
313 	},
314 };
315 
timer_sysctl_init(void)316 static int __init timer_sysctl_init(void)
317 {
318 	register_sysctl("kernel", timer_sysctl);
319 	return 0;
320 }
321 device_initcall(timer_sysctl_init);
322 #endif /* CONFIG_SYSCTL */
323 #else /* CONFIG_SMP */
timers_update_migration(void)324 static inline void timers_update_migration(void) { }
325 #endif /* !CONFIG_SMP */
326 
timer_update_keys(struct work_struct * work)327 static void timer_update_keys(struct work_struct *work)
328 {
329 	mutex_lock(&timer_keys_mutex);
330 	timers_update_migration();
331 	static_branch_enable(&timers_nohz_active);
332 	mutex_unlock(&timer_keys_mutex);
333 }
334 
timers_update_nohz(void)335 void timers_update_nohz(void)
336 {
337 	schedule_work(&timer_update_work);
338 }
339 
is_timers_nohz_active(void)340 static inline bool is_timers_nohz_active(void)
341 {
342 	return static_branch_unlikely(&timers_nohz_active);
343 }
344 #else
is_timers_nohz_active(void)345 static inline bool is_timers_nohz_active(void) { return false; }
346 #endif /* NO_HZ_COMMON */
347 
round_jiffies_common(unsigned long j,int cpu,bool force_up)348 static unsigned long round_jiffies_common(unsigned long j, int cpu,
349 		bool force_up)
350 {
351 	int rem;
352 	unsigned long original = j;
353 
354 	/*
355 	 * We don't want all cpus firing their timers at once hitting the
356 	 * same lock or cachelines, so we skew each extra cpu with an extra
357 	 * 3 jiffies. This 3 jiffies came originally from the mm/ code which
358 	 * already did this.
359 	 * The skew is done by adding 3*cpunr, then round, then subtract this
360 	 * extra offset again.
361 	 */
362 	j += cpu * 3;
363 
364 	rem = j % HZ;
365 
366 	/*
367 	 * If the target jiffy is just after a whole second (which can happen
368 	 * due to delays of the timer irq, long irq off times etc etc) then
369 	 * we should round down to the whole second, not up. Use 1/4th second
370 	 * as cutoff for this rounding as an extreme upper bound for this.
371 	 * But never round down if @force_up is set.
372 	 */
373 	if (rem < HZ/4 && !force_up) /* round down */
374 		j = j - rem;
375 	else /* round up */
376 		j = j - rem + HZ;
377 
378 	/* now that we have rounded, subtract the extra skew again */
379 	j -= cpu * 3;
380 
381 	/*
382 	 * Make sure j is still in the future. Otherwise return the
383 	 * unmodified value.
384 	 */
385 	return time_is_after_jiffies(j) ? j : original;
386 }
387 
388 /**
389  * __round_jiffies - function to round jiffies to a full second
390  * @j: the time in (absolute) jiffies that should be rounded
391  * @cpu: the processor number on which the timeout will happen
392  *
393  * __round_jiffies() rounds an absolute time in the future (in jiffies)
394  * up or down to (approximately) full seconds. This is useful for timers
395  * for which the exact time they fire does not matter too much, as long as
396  * they fire approximately every X seconds.
397  *
398  * By rounding these timers to whole seconds, all such timers will fire
399  * at the same time, rather than at various times spread out. The goal
400  * of this is to have the CPU wake up less, which saves power.
401  *
402  * The exact rounding is skewed for each processor to avoid all
403  * processors firing at the exact same time, which could lead
404  * to lock contention or spurious cache line bouncing.
405  *
406  * The return value is the rounded version of the @j parameter.
407  */
__round_jiffies(unsigned long j,int cpu)408 unsigned long __round_jiffies(unsigned long j, int cpu)
409 {
410 	return round_jiffies_common(j, cpu, false);
411 }
412 EXPORT_SYMBOL_GPL(__round_jiffies);
413 
414 /**
415  * __round_jiffies_relative - function to round jiffies to a full second
416  * @j: the time in (relative) jiffies that should be rounded
417  * @cpu: the processor number on which the timeout will happen
418  *
419  * __round_jiffies_relative() rounds a time delta  in the future (in jiffies)
420  * up or down to (approximately) full seconds. This is useful for timers
421  * for which the exact time they fire does not matter too much, as long as
422  * they fire approximately every X seconds.
423  *
424  * By rounding these timers to whole seconds, all such timers will fire
425  * at the same time, rather than at various times spread out. The goal
426  * of this is to have the CPU wake up less, which saves power.
427  *
428  * The exact rounding is skewed for each processor to avoid all
429  * processors firing at the exact same time, which could lead
430  * to lock contention or spurious cache line bouncing.
431  *
432  * The return value is the rounded version of the @j parameter.
433  */
__round_jiffies_relative(unsigned long j,int cpu)434 unsigned long __round_jiffies_relative(unsigned long j, int cpu)
435 {
436 	unsigned long j0 = jiffies;
437 
438 	/* Use j0 because jiffies might change while we run */
439 	return round_jiffies_common(j + j0, cpu, false) - j0;
440 }
441 EXPORT_SYMBOL_GPL(__round_jiffies_relative);
442 
443 /**
444  * round_jiffies - function to round jiffies to a full second
445  * @j: the time in (absolute) jiffies that should be rounded
446  *
447  * round_jiffies() rounds an absolute time in the future (in jiffies)
448  * up or down to (approximately) full seconds. This is useful for timers
449  * for which the exact time they fire does not matter too much, as long as
450  * they fire approximately every X seconds.
451  *
452  * By rounding these timers to whole seconds, all such timers will fire
453  * at the same time, rather than at various times spread out. The goal
454  * of this is to have the CPU wake up less, which saves power.
455  *
456  * The return value is the rounded version of the @j parameter.
457  */
round_jiffies(unsigned long j)458 unsigned long round_jiffies(unsigned long j)
459 {
460 	return round_jiffies_common(j, raw_smp_processor_id(), false);
461 }
462 EXPORT_SYMBOL_GPL(round_jiffies);
463 
464 /**
465  * round_jiffies_relative - function to round jiffies to a full second
466  * @j: the time in (relative) jiffies that should be rounded
467  *
468  * round_jiffies_relative() rounds a time delta  in the future (in jiffies)
469  * up or down to (approximately) full seconds. This is useful for timers
470  * for which the exact time they fire does not matter too much, as long as
471  * they fire approximately every X seconds.
472  *
473  * By rounding these timers to whole seconds, all such timers will fire
474  * at the same time, rather than at various times spread out. The goal
475  * of this is to have the CPU wake up less, which saves power.
476  *
477  * The return value is the rounded version of the @j parameter.
478  */
round_jiffies_relative(unsigned long j)479 unsigned long round_jiffies_relative(unsigned long j)
480 {
481 	return __round_jiffies_relative(j, raw_smp_processor_id());
482 }
483 EXPORT_SYMBOL_GPL(round_jiffies_relative);
484 
485 /**
486  * __round_jiffies_up - function to round jiffies up to a full second
487  * @j: the time in (absolute) jiffies that should be rounded
488  * @cpu: the processor number on which the timeout will happen
489  *
490  * This is the same as __round_jiffies() except that it will never
491  * round down.  This is useful for timeouts for which the exact time
492  * of firing does not matter too much, as long as they don't fire too
493  * early.
494  */
__round_jiffies_up(unsigned long j,int cpu)495 unsigned long __round_jiffies_up(unsigned long j, int cpu)
496 {
497 	return round_jiffies_common(j, cpu, true);
498 }
499 EXPORT_SYMBOL_GPL(__round_jiffies_up);
500 
501 /**
502  * __round_jiffies_up_relative - function to round jiffies up to a full second
503  * @j: the time in (relative) jiffies that should be rounded
504  * @cpu: the processor number on which the timeout will happen
505  *
506  * This is the same as __round_jiffies_relative() except that it will never
507  * round down.  This is useful for timeouts for which the exact time
508  * of firing does not matter too much, as long as they don't fire too
509  * early.
510  */
__round_jiffies_up_relative(unsigned long j,int cpu)511 unsigned long __round_jiffies_up_relative(unsigned long j, int cpu)
512 {
513 	unsigned long j0 = jiffies;
514 
515 	/* Use j0 because jiffies might change while we run */
516 	return round_jiffies_common(j + j0, cpu, true) - j0;
517 }
518 EXPORT_SYMBOL_GPL(__round_jiffies_up_relative);
519 
520 /**
521  * round_jiffies_up - function to round jiffies up to a full second
522  * @j: the time in (absolute) jiffies that should be rounded
523  *
524  * This is the same as round_jiffies() except that it will never
525  * round down.  This is useful for timeouts for which the exact time
526  * of firing does not matter too much, as long as they don't fire too
527  * early.
528  */
round_jiffies_up(unsigned long j)529 unsigned long round_jiffies_up(unsigned long j)
530 {
531 	return round_jiffies_common(j, raw_smp_processor_id(), true);
532 }
533 EXPORT_SYMBOL_GPL(round_jiffies_up);
534 
535 /**
536  * round_jiffies_up_relative - function to round jiffies up to a full second
537  * @j: the time in (relative) jiffies that should be rounded
538  *
539  * This is the same as round_jiffies_relative() except that it will never
540  * round down.  This is useful for timeouts for which the exact time
541  * of firing does not matter too much, as long as they don't fire too
542  * early.
543  */
round_jiffies_up_relative(unsigned long j)544 unsigned long round_jiffies_up_relative(unsigned long j)
545 {
546 	return __round_jiffies_up_relative(j, raw_smp_processor_id());
547 }
548 EXPORT_SYMBOL_GPL(round_jiffies_up_relative);
549 
550 
timer_get_idx(struct timer_list * timer)551 static inline unsigned int timer_get_idx(struct timer_list *timer)
552 {
553 	return (timer->flags & TIMER_ARRAYMASK) >> TIMER_ARRAYSHIFT;
554 }
555 
timer_set_idx(struct timer_list * timer,unsigned int idx)556 static inline void timer_set_idx(struct timer_list *timer, unsigned int idx)
557 {
558 	timer->flags = (timer->flags & ~TIMER_ARRAYMASK) |
559 			idx << TIMER_ARRAYSHIFT;
560 }
561 
562 /*
563  * Helper function to calculate the array index for a given expiry
564  * time.
565  */
calc_index(unsigned long expires,unsigned lvl,unsigned long * bucket_expiry)566 static inline unsigned calc_index(unsigned long expires, unsigned lvl,
567 				  unsigned long *bucket_expiry)
568 {
569 
570 	/*
571 	 * The timer wheel has to guarantee that a timer does not fire
572 	 * early. Early expiry can happen due to:
573 	 * - Timer is armed at the edge of a tick
574 	 * - Truncation of the expiry time in the outer wheel levels
575 	 *
576 	 * Round up with level granularity to prevent this.
577 	 */
578 	expires = (expires >> LVL_SHIFT(lvl)) + 1;
579 	*bucket_expiry = expires << LVL_SHIFT(lvl);
580 	return LVL_OFFS(lvl) + (expires & LVL_MASK);
581 }
582 
calc_wheel_index(unsigned long expires,unsigned long clk,unsigned long * bucket_expiry)583 static int calc_wheel_index(unsigned long expires, unsigned long clk,
584 			    unsigned long *bucket_expiry)
585 {
586 	unsigned long delta = expires - clk;
587 	unsigned int idx;
588 
589 	if (delta < LVL_START(1)) {
590 		idx = calc_index(expires, 0, bucket_expiry);
591 	} else if (delta < LVL_START(2)) {
592 		idx = calc_index(expires, 1, bucket_expiry);
593 	} else if (delta < LVL_START(3)) {
594 		idx = calc_index(expires, 2, bucket_expiry);
595 	} else if (delta < LVL_START(4)) {
596 		idx = calc_index(expires, 3, bucket_expiry);
597 	} else if (delta < LVL_START(5)) {
598 		idx = calc_index(expires, 4, bucket_expiry);
599 	} else if (delta < LVL_START(6)) {
600 		idx = calc_index(expires, 5, bucket_expiry);
601 	} else if (delta < LVL_START(7)) {
602 		idx = calc_index(expires, 6, bucket_expiry);
603 	} else if (LVL_DEPTH > 8 && delta < LVL_START(8)) {
604 		idx = calc_index(expires, 7, bucket_expiry);
605 	} else if ((long) delta < 0) {
606 		idx = clk & LVL_MASK;
607 		*bucket_expiry = clk;
608 	} else {
609 		/*
610 		 * Force expire obscene large timeouts to expire at the
611 		 * capacity limit of the wheel.
612 		 */
613 		if (delta >= WHEEL_TIMEOUT_CUTOFF)
614 			expires = clk + WHEEL_TIMEOUT_MAX;
615 
616 		idx = calc_index(expires, LVL_DEPTH - 1, bucket_expiry);
617 	}
618 	return idx;
619 }
620 
621 static void
trigger_dyntick_cpu(struct timer_base * base,struct timer_list * timer)622 trigger_dyntick_cpu(struct timer_base *base, struct timer_list *timer)
623 {
624 	/*
625 	 * Deferrable timers do not prevent the CPU from entering dynticks and
626 	 * are not taken into account on the idle/nohz_full path. An IPI when a
627 	 * new deferrable timer is enqueued will wake up the remote CPU but
628 	 * nothing will be done with the deferrable timer base. Therefore skip
629 	 * the remote IPI for deferrable timers completely.
630 	 */
631 	if (!is_timers_nohz_active() || timer->flags & TIMER_DEFERRABLE)
632 		return;
633 
634 	/*
635 	 * We might have to IPI the remote CPU if the base is idle and the
636 	 * timer is pinned. If it is a non pinned timer, it is only queued
637 	 * on the remote CPU, when timer was running during queueing. Then
638 	 * everything is handled by remote CPU anyway. If the other CPU is
639 	 * on the way to idle then it can't set base->is_idle as we hold
640 	 * the base lock:
641 	 */
642 	if (base->is_idle) {
643 		WARN_ON_ONCE(!(timer->flags & TIMER_PINNED ||
644 			       tick_nohz_full_cpu(base->cpu)));
645 		wake_up_nohz_cpu(base->cpu);
646 	}
647 }
648 
649 /*
650  * Enqueue the timer into the hash bucket, mark it pending in
651  * the bitmap, store the index in the timer flags then wake up
652  * the target CPU if needed.
653  */
enqueue_timer(struct timer_base * base,struct timer_list * timer,unsigned int idx,unsigned long bucket_expiry)654 static void enqueue_timer(struct timer_base *base, struct timer_list *timer,
655 			  unsigned int idx, unsigned long bucket_expiry)
656 {
657 
658 	hlist_add_head(&timer->entry, base->vectors + idx);
659 	__set_bit(idx, base->pending_map);
660 	timer_set_idx(timer, idx);
661 
662 	trace_timer_start(timer, bucket_expiry);
663 
664 	/*
665 	 * Check whether this is the new first expiring timer. The
666 	 * effective expiry time of the timer is required here
667 	 * (bucket_expiry) instead of timer->expires.
668 	 */
669 	if (time_before(bucket_expiry, base->next_expiry)) {
670 		/*
671 		 * Set the next expiry time and kick the CPU so it
672 		 * can reevaluate the wheel:
673 		 */
674 		WRITE_ONCE(base->next_expiry, bucket_expiry);
675 		base->timers_pending = true;
676 		base->next_expiry_recalc = false;
677 		trigger_dyntick_cpu(base, timer);
678 	}
679 }
680 
internal_add_timer(struct timer_base * base,struct timer_list * timer)681 static void internal_add_timer(struct timer_base *base, struct timer_list *timer)
682 {
683 	unsigned long bucket_expiry;
684 	unsigned int idx;
685 
686 	idx = calc_wheel_index(timer->expires, base->clk, &bucket_expiry);
687 	enqueue_timer(base, timer, idx, bucket_expiry);
688 }
689 
690 #ifdef CONFIG_DEBUG_OBJECTS_TIMERS
691 
692 static const struct debug_obj_descr timer_debug_descr;
693 
694 struct timer_hint {
695 	void	(*function)(struct timer_list *t);
696 	long	offset;
697 };
698 
699 #define TIMER_HINT(fn, container, timr, hintfn)			\
700 	{							\
701 		.function = fn,					\
702 		.offset	  = offsetof(container, hintfn) -	\
703 			    offsetof(container, timr)		\
704 	}
705 
706 static const struct timer_hint timer_hints[] = {
707 	TIMER_HINT(delayed_work_timer_fn,
708 		   struct delayed_work, timer, work.func),
709 	TIMER_HINT(kthread_delayed_work_timer_fn,
710 		   struct kthread_delayed_work, timer, work.func),
711 };
712 
timer_debug_hint(void * addr)713 static void *timer_debug_hint(void *addr)
714 {
715 	struct timer_list *timer = addr;
716 	int i;
717 
718 	for (i = 0; i < ARRAY_SIZE(timer_hints); i++) {
719 		if (timer_hints[i].function == timer->function) {
720 			void (**fn)(void) = addr + timer_hints[i].offset;
721 
722 			return *fn;
723 		}
724 	}
725 
726 	return timer->function;
727 }
728 
timer_is_static_object(void * addr)729 static bool timer_is_static_object(void *addr)
730 {
731 	struct timer_list *timer = addr;
732 
733 	return (timer->entry.pprev == NULL &&
734 		timer->entry.next == TIMER_ENTRY_STATIC);
735 }
736 
737 /*
738  * timer_fixup_init is called when:
739  * - an active object is initialized
740  */
timer_fixup_init(void * addr,enum debug_obj_state state)741 static bool timer_fixup_init(void *addr, enum debug_obj_state state)
742 {
743 	struct timer_list *timer = addr;
744 
745 	switch (state) {
746 	case ODEBUG_STATE_ACTIVE:
747 		del_timer_sync(timer);
748 		debug_object_init(timer, &timer_debug_descr);
749 		return true;
750 	default:
751 		return false;
752 	}
753 }
754 
755 /* Stub timer callback for improperly used timers. */
stub_timer(struct timer_list * unused)756 static void stub_timer(struct timer_list *unused)
757 {
758 	WARN_ON(1);
759 }
760 
761 /*
762  * timer_fixup_activate is called when:
763  * - an active object is activated
764  * - an unknown non-static object is activated
765  */
timer_fixup_activate(void * addr,enum debug_obj_state state)766 static bool timer_fixup_activate(void *addr, enum debug_obj_state state)
767 {
768 	struct timer_list *timer = addr;
769 
770 	switch (state) {
771 	case ODEBUG_STATE_NOTAVAILABLE:
772 		timer_setup(timer, stub_timer, 0);
773 		return true;
774 
775 	case ODEBUG_STATE_ACTIVE:
776 		WARN_ON(1);
777 		fallthrough;
778 	default:
779 		return false;
780 	}
781 }
782 
783 /*
784  * timer_fixup_free is called when:
785  * - an active object is freed
786  */
timer_fixup_free(void * addr,enum debug_obj_state state)787 static bool timer_fixup_free(void *addr, enum debug_obj_state state)
788 {
789 	struct timer_list *timer = addr;
790 
791 	switch (state) {
792 	case ODEBUG_STATE_ACTIVE:
793 		del_timer_sync(timer);
794 		debug_object_free(timer, &timer_debug_descr);
795 		return true;
796 	default:
797 		return false;
798 	}
799 }
800 
801 /*
802  * timer_fixup_assert_init is called when:
803  * - an untracked/uninit-ed object is found
804  */
timer_fixup_assert_init(void * addr,enum debug_obj_state state)805 static bool timer_fixup_assert_init(void *addr, enum debug_obj_state state)
806 {
807 	struct timer_list *timer = addr;
808 
809 	switch (state) {
810 	case ODEBUG_STATE_NOTAVAILABLE:
811 		timer_setup(timer, stub_timer, 0);
812 		return true;
813 	default:
814 		return false;
815 	}
816 }
817 
818 static const struct debug_obj_descr timer_debug_descr = {
819 	.name			= "timer_list",
820 	.debug_hint		= timer_debug_hint,
821 	.is_static_object	= timer_is_static_object,
822 	.fixup_init		= timer_fixup_init,
823 	.fixup_activate		= timer_fixup_activate,
824 	.fixup_free		= timer_fixup_free,
825 	.fixup_assert_init	= timer_fixup_assert_init,
826 };
827 
debug_timer_init(struct timer_list * timer)828 static inline void debug_timer_init(struct timer_list *timer)
829 {
830 	debug_object_init(timer, &timer_debug_descr);
831 }
832 
debug_timer_activate(struct timer_list * timer)833 static inline void debug_timer_activate(struct timer_list *timer)
834 {
835 	debug_object_activate(timer, &timer_debug_descr);
836 }
837 
debug_timer_deactivate(struct timer_list * timer)838 static inline void debug_timer_deactivate(struct timer_list *timer)
839 {
840 	debug_object_deactivate(timer, &timer_debug_descr);
841 }
842 
debug_timer_assert_init(struct timer_list * timer)843 static inline void debug_timer_assert_init(struct timer_list *timer)
844 {
845 	debug_object_assert_init(timer, &timer_debug_descr);
846 }
847 
848 static void do_init_timer(struct timer_list *timer,
849 			  void (*func)(struct timer_list *),
850 			  unsigned int flags,
851 			  const char *name, struct lock_class_key *key);
852 
init_timer_on_stack_key(struct timer_list * timer,void (* func)(struct timer_list *),unsigned int flags,const char * name,struct lock_class_key * key)853 void init_timer_on_stack_key(struct timer_list *timer,
854 			     void (*func)(struct timer_list *),
855 			     unsigned int flags,
856 			     const char *name, struct lock_class_key *key)
857 {
858 	debug_object_init_on_stack(timer, &timer_debug_descr);
859 	do_init_timer(timer, func, flags, name, key);
860 }
861 EXPORT_SYMBOL_GPL(init_timer_on_stack_key);
862 
destroy_timer_on_stack(struct timer_list * timer)863 void destroy_timer_on_stack(struct timer_list *timer)
864 {
865 	debug_object_free(timer, &timer_debug_descr);
866 }
867 EXPORT_SYMBOL_GPL(destroy_timer_on_stack);
868 
869 #else
debug_timer_init(struct timer_list * timer)870 static inline void debug_timer_init(struct timer_list *timer) { }
debug_timer_activate(struct timer_list * timer)871 static inline void debug_timer_activate(struct timer_list *timer) { }
debug_timer_deactivate(struct timer_list * timer)872 static inline void debug_timer_deactivate(struct timer_list *timer) { }
debug_timer_assert_init(struct timer_list * timer)873 static inline void debug_timer_assert_init(struct timer_list *timer) { }
874 #endif
875 
debug_init(struct timer_list * timer)876 static inline void debug_init(struct timer_list *timer)
877 {
878 	debug_timer_init(timer);
879 	trace_timer_init(timer);
880 }
881 
debug_deactivate(struct timer_list * timer)882 static inline void debug_deactivate(struct timer_list *timer)
883 {
884 	debug_timer_deactivate(timer);
885 	trace_timer_cancel(timer);
886 }
887 
debug_assert_init(struct timer_list * timer)888 static inline void debug_assert_init(struct timer_list *timer)
889 {
890 	debug_timer_assert_init(timer);
891 }
892 
do_init_timer(struct timer_list * timer,void (* func)(struct timer_list *),unsigned int flags,const char * name,struct lock_class_key * key)893 static void do_init_timer(struct timer_list *timer,
894 			  void (*func)(struct timer_list *),
895 			  unsigned int flags,
896 			  const char *name, struct lock_class_key *key)
897 {
898 	timer->entry.pprev = NULL;
899 	timer->function = func;
900 	if (WARN_ON_ONCE(flags & ~TIMER_INIT_FLAGS))
901 		flags &= TIMER_INIT_FLAGS;
902 	timer->flags = flags | raw_smp_processor_id();
903 	lockdep_init_map(&timer->lockdep_map, name, key, 0);
904 }
905 
906 /**
907  * init_timer_key - initialize a timer
908  * @timer: the timer to be initialized
909  * @func: timer callback function
910  * @flags: timer flags
911  * @name: name of the timer
912  * @key: lockdep class key of the fake lock used for tracking timer
913  *       sync lock dependencies
914  *
915  * init_timer_key() must be done to a timer prior to calling *any* of the
916  * other timer functions.
917  */
init_timer_key(struct timer_list * timer,void (* func)(struct timer_list *),unsigned int flags,const char * name,struct lock_class_key * key)918 void init_timer_key(struct timer_list *timer,
919 		    void (*func)(struct timer_list *), unsigned int flags,
920 		    const char *name, struct lock_class_key *key)
921 {
922 	debug_init(timer);
923 	do_init_timer(timer, func, flags, name, key);
924 }
925 EXPORT_SYMBOL(init_timer_key);
926 
detach_timer(struct timer_list * timer,bool clear_pending)927 static inline void detach_timer(struct timer_list *timer, bool clear_pending)
928 {
929 	struct hlist_node *entry = &timer->entry;
930 
931 	debug_deactivate(timer);
932 
933 	__hlist_del(entry);
934 	if (clear_pending)
935 		entry->pprev = NULL;
936 	entry->next = LIST_POISON2;
937 }
938 
detach_if_pending(struct timer_list * timer,struct timer_base * base,bool clear_pending)939 static int detach_if_pending(struct timer_list *timer, struct timer_base *base,
940 			     bool clear_pending)
941 {
942 	unsigned idx = timer_get_idx(timer);
943 
944 	if (!timer_pending(timer))
945 		return 0;
946 
947 	if (hlist_is_singular_node(&timer->entry, base->vectors + idx)) {
948 		__clear_bit(idx, base->pending_map);
949 		base->next_expiry_recalc = true;
950 	}
951 
952 	detach_timer(timer, clear_pending);
953 	return 1;
954 }
955 
get_timer_cpu_base(u32 tflags,u32 cpu)956 static inline struct timer_base *get_timer_cpu_base(u32 tflags, u32 cpu)
957 {
958 	int index = tflags & TIMER_PINNED ? BASE_LOCAL : BASE_GLOBAL;
959 	struct timer_base *base;
960 
961 	base = per_cpu_ptr(&timer_bases[index], cpu);
962 
963 	/*
964 	 * If the timer is deferrable and NO_HZ_COMMON is set then we need
965 	 * to use the deferrable base.
966 	 */
967 	if (IS_ENABLED(CONFIG_NO_HZ_COMMON) && (tflags & TIMER_DEFERRABLE))
968 		base = per_cpu_ptr(&timer_bases[BASE_DEF], cpu);
969 	return base;
970 }
971 
get_timer_this_cpu_base(u32 tflags)972 static inline struct timer_base *get_timer_this_cpu_base(u32 tflags)
973 {
974 	int index = tflags & TIMER_PINNED ? BASE_LOCAL : BASE_GLOBAL;
975 	struct timer_base *base;
976 
977 	base = this_cpu_ptr(&timer_bases[index]);
978 
979 	/*
980 	 * If the timer is deferrable and NO_HZ_COMMON is set then we need
981 	 * to use the deferrable base.
982 	 */
983 	if (IS_ENABLED(CONFIG_NO_HZ_COMMON) && (tflags & TIMER_DEFERRABLE))
984 		base = this_cpu_ptr(&timer_bases[BASE_DEF]);
985 	return base;
986 }
987 
get_timer_base(u32 tflags)988 static inline struct timer_base *get_timer_base(u32 tflags)
989 {
990 	return get_timer_cpu_base(tflags, tflags & TIMER_CPUMASK);
991 }
992 
__forward_timer_base(struct timer_base * base,unsigned long basej)993 static inline void __forward_timer_base(struct timer_base *base,
994 					unsigned long basej)
995 {
996 	/*
997 	 * Check whether we can forward the base. We can only do that when
998 	 * @basej is past base->clk otherwise we might rewind base->clk.
999 	 */
1000 	if (time_before_eq(basej, base->clk))
1001 		return;
1002 
1003 	/*
1004 	 * If the next expiry value is > jiffies, then we fast forward to
1005 	 * jiffies otherwise we forward to the next expiry value.
1006 	 */
1007 	if (time_after(base->next_expiry, basej)) {
1008 		base->clk = basej;
1009 	} else {
1010 		if (WARN_ON_ONCE(time_before(base->next_expiry, base->clk)))
1011 			return;
1012 		base->clk = base->next_expiry;
1013 	}
1014 
1015 }
1016 
forward_timer_base(struct timer_base * base)1017 static inline void forward_timer_base(struct timer_base *base)
1018 {
1019 	__forward_timer_base(base, READ_ONCE(jiffies));
1020 }
1021 
1022 /*
1023  * We are using hashed locking: Holding per_cpu(timer_bases[x]).lock means
1024  * that all timers which are tied to this base are locked, and the base itself
1025  * is locked too.
1026  *
1027  * So __run_timers/migrate_timers can safely modify all timers which could
1028  * be found in the base->vectors array.
1029  *
1030  * When a timer is migrating then the TIMER_MIGRATING flag is set and we need
1031  * to wait until the migration is done.
1032  */
lock_timer_base(struct timer_list * timer,unsigned long * flags)1033 static struct timer_base *lock_timer_base(struct timer_list *timer,
1034 					  unsigned long *flags)
1035 	__acquires(timer->base->lock)
1036 {
1037 	for (;;) {
1038 		struct timer_base *base;
1039 		u32 tf;
1040 
1041 		/*
1042 		 * We need to use READ_ONCE() here, otherwise the compiler
1043 		 * might re-read @tf between the check for TIMER_MIGRATING
1044 		 * and spin_lock().
1045 		 */
1046 		tf = READ_ONCE(timer->flags);
1047 
1048 		if (!(tf & TIMER_MIGRATING)) {
1049 			base = get_timer_base(tf);
1050 			raw_spin_lock_irqsave(&base->lock, *flags);
1051 			if (timer->flags == tf)
1052 				return base;
1053 			raw_spin_unlock_irqrestore(&base->lock, *flags);
1054 		}
1055 		cpu_relax();
1056 	}
1057 }
1058 
1059 #define MOD_TIMER_PENDING_ONLY		0x01
1060 #define MOD_TIMER_REDUCE		0x02
1061 #define MOD_TIMER_NOTPENDING		0x04
1062 
1063 static inline int
__mod_timer(struct timer_list * timer,unsigned long expires,unsigned int options)1064 __mod_timer(struct timer_list *timer, unsigned long expires, unsigned int options)
1065 {
1066 	unsigned long clk = 0, flags, bucket_expiry;
1067 	struct timer_base *base, *new_base;
1068 	unsigned int idx = UINT_MAX;
1069 	int ret = 0;
1070 
1071 	debug_assert_init(timer);
1072 
1073 	/*
1074 	 * This is a common optimization triggered by the networking code - if
1075 	 * the timer is re-modified to have the same timeout or ends up in the
1076 	 * same array bucket then just return:
1077 	 */
1078 	if (!(options & MOD_TIMER_NOTPENDING) && timer_pending(timer)) {
1079 		/*
1080 		 * The downside of this optimization is that it can result in
1081 		 * larger granularity than you would get from adding a new
1082 		 * timer with this expiry.
1083 		 */
1084 		long diff = timer->expires - expires;
1085 
1086 		if (!diff)
1087 			return 1;
1088 		if (options & MOD_TIMER_REDUCE && diff <= 0)
1089 			return 1;
1090 
1091 		/*
1092 		 * We lock timer base and calculate the bucket index right
1093 		 * here. If the timer ends up in the same bucket, then we
1094 		 * just update the expiry time and avoid the whole
1095 		 * dequeue/enqueue dance.
1096 		 */
1097 		base = lock_timer_base(timer, &flags);
1098 		/*
1099 		 * Has @timer been shutdown? This needs to be evaluated
1100 		 * while holding base lock to prevent a race against the
1101 		 * shutdown code.
1102 		 */
1103 		if (!timer->function)
1104 			goto out_unlock;
1105 
1106 		forward_timer_base(base);
1107 
1108 		if (timer_pending(timer) && (options & MOD_TIMER_REDUCE) &&
1109 		    time_before_eq(timer->expires, expires)) {
1110 			ret = 1;
1111 			goto out_unlock;
1112 		}
1113 
1114 		clk = base->clk;
1115 		idx = calc_wheel_index(expires, clk, &bucket_expiry);
1116 
1117 		/*
1118 		 * Retrieve and compare the array index of the pending
1119 		 * timer. If it matches set the expiry to the new value so a
1120 		 * subsequent call will exit in the expires check above.
1121 		 */
1122 		if (idx == timer_get_idx(timer)) {
1123 			if (!(options & MOD_TIMER_REDUCE))
1124 				timer->expires = expires;
1125 			else if (time_after(timer->expires, expires))
1126 				timer->expires = expires;
1127 			ret = 1;
1128 			goto out_unlock;
1129 		}
1130 	} else {
1131 		base = lock_timer_base(timer, &flags);
1132 		/*
1133 		 * Has @timer been shutdown? This needs to be evaluated
1134 		 * while holding base lock to prevent a race against the
1135 		 * shutdown code.
1136 		 */
1137 		if (!timer->function)
1138 			goto out_unlock;
1139 
1140 		forward_timer_base(base);
1141 	}
1142 
1143 	ret = detach_if_pending(timer, base, false);
1144 	if (!ret && (options & MOD_TIMER_PENDING_ONLY))
1145 		goto out_unlock;
1146 
1147 	new_base = get_timer_this_cpu_base(timer->flags);
1148 
1149 	if (base != new_base) {
1150 		/*
1151 		 * We are trying to schedule the timer on the new base.
1152 		 * However we can't change timer's base while it is running,
1153 		 * otherwise timer_delete_sync() can't detect that the timer's
1154 		 * handler yet has not finished. This also guarantees that the
1155 		 * timer is serialized wrt itself.
1156 		 */
1157 		if (likely(base->running_timer != timer)) {
1158 			/* See the comment in lock_timer_base() */
1159 			timer->flags |= TIMER_MIGRATING;
1160 
1161 			raw_spin_unlock(&base->lock);
1162 			base = new_base;
1163 			raw_spin_lock(&base->lock);
1164 			WRITE_ONCE(timer->flags,
1165 				   (timer->flags & ~TIMER_BASEMASK) | base->cpu);
1166 			forward_timer_base(base);
1167 		}
1168 	}
1169 
1170 	debug_timer_activate(timer);
1171 
1172 	timer->expires = expires;
1173 	/*
1174 	 * If 'idx' was calculated above and the base time did not advance
1175 	 * between calculating 'idx' and possibly switching the base, only
1176 	 * enqueue_timer() is required. Otherwise we need to (re)calculate
1177 	 * the wheel index via internal_add_timer().
1178 	 */
1179 	if (idx != UINT_MAX && clk == base->clk)
1180 		enqueue_timer(base, timer, idx, bucket_expiry);
1181 	else
1182 		internal_add_timer(base, timer);
1183 
1184 out_unlock:
1185 	raw_spin_unlock_irqrestore(&base->lock, flags);
1186 
1187 	return ret;
1188 }
1189 
1190 /**
1191  * mod_timer_pending - Modify a pending timer's timeout
1192  * @timer:	The pending timer to be modified
1193  * @expires:	New absolute timeout in jiffies
1194  *
1195  * mod_timer_pending() is the same for pending timers as mod_timer(), but
1196  * will not activate inactive timers.
1197  *
1198  * If @timer->function == NULL then the start operation is silently
1199  * discarded.
1200  *
1201  * Return:
1202  * * %0 - The timer was inactive and not modified or was in
1203  *	  shutdown state and the operation was discarded
1204  * * %1 - The timer was active and requeued to expire at @expires
1205  */
mod_timer_pending(struct timer_list * timer,unsigned long expires)1206 int mod_timer_pending(struct timer_list *timer, unsigned long expires)
1207 {
1208 	return __mod_timer(timer, expires, MOD_TIMER_PENDING_ONLY);
1209 }
1210 EXPORT_SYMBOL(mod_timer_pending);
1211 
1212 /**
1213  * mod_timer - Modify a timer's timeout
1214  * @timer:	The timer to be modified
1215  * @expires:	New absolute timeout in jiffies
1216  *
1217  * mod_timer(timer, expires) is equivalent to:
1218  *
1219  *     del_timer(timer); timer->expires = expires; add_timer(timer);
1220  *
1221  * mod_timer() is more efficient than the above open coded sequence. In
1222  * case that the timer is inactive, the del_timer() part is a NOP. The
1223  * timer is in any case activated with the new expiry time @expires.
1224  *
1225  * Note that if there are multiple unserialized concurrent users of the
1226  * same timer, then mod_timer() is the only safe way to modify the timeout,
1227  * since add_timer() cannot modify an already running timer.
1228  *
1229  * If @timer->function == NULL then the start operation is silently
1230  * discarded. In this case the return value is 0 and meaningless.
1231  *
1232  * Return:
1233  * * %0 - The timer was inactive and started or was in shutdown
1234  *	  state and the operation was discarded
1235  * * %1 - The timer was active and requeued to expire at @expires or
1236  *	  the timer was active and not modified because @expires did
1237  *	  not change the effective expiry time
1238  */
mod_timer(struct timer_list * timer,unsigned long expires)1239 int mod_timer(struct timer_list *timer, unsigned long expires)
1240 {
1241 	return __mod_timer(timer, expires, 0);
1242 }
1243 EXPORT_SYMBOL(mod_timer);
1244 
1245 /**
1246  * timer_reduce - Modify a timer's timeout if it would reduce the timeout
1247  * @timer:	The timer to be modified
1248  * @expires:	New absolute timeout in jiffies
1249  *
1250  * timer_reduce() is very similar to mod_timer(), except that it will only
1251  * modify an enqueued timer if that would reduce the expiration time. If
1252  * @timer is not enqueued it starts the timer.
1253  *
1254  * If @timer->function == NULL then the start operation is silently
1255  * discarded.
1256  *
1257  * Return:
1258  * * %0 - The timer was inactive and started or was in shutdown
1259  *	  state and the operation was discarded
1260  * * %1 - The timer was active and requeued to expire at @expires or
1261  *	  the timer was active and not modified because @expires
1262  *	  did not change the effective expiry time such that the
1263  *	  timer would expire earlier than already scheduled
1264  */
timer_reduce(struct timer_list * timer,unsigned long expires)1265 int timer_reduce(struct timer_list *timer, unsigned long expires)
1266 {
1267 	return __mod_timer(timer, expires, MOD_TIMER_REDUCE);
1268 }
1269 EXPORT_SYMBOL(timer_reduce);
1270 
1271 /**
1272  * add_timer - Start a timer
1273  * @timer:	The timer to be started
1274  *
1275  * Start @timer to expire at @timer->expires in the future. @timer->expires
1276  * is the absolute expiry time measured in 'jiffies'. When the timer expires
1277  * timer->function(timer) will be invoked from soft interrupt context.
1278  *
1279  * The @timer->expires and @timer->function fields must be set prior
1280  * to calling this function.
1281  *
1282  * If @timer->function == NULL then the start operation is silently
1283  * discarded.
1284  *
1285  * If @timer->expires is already in the past @timer will be queued to
1286  * expire at the next timer tick.
1287  *
1288  * This can only operate on an inactive timer. Attempts to invoke this on
1289  * an active timer are rejected with a warning.
1290  */
add_timer(struct timer_list * timer)1291 void add_timer(struct timer_list *timer)
1292 {
1293 	if (WARN_ON_ONCE(timer_pending(timer)))
1294 		return;
1295 	__mod_timer(timer, timer->expires, MOD_TIMER_NOTPENDING);
1296 }
1297 EXPORT_SYMBOL(add_timer);
1298 
1299 /**
1300  * add_timer_local() - Start a timer on the local CPU
1301  * @timer:	The timer to be started
1302  *
1303  * Same as add_timer() except that the timer flag TIMER_PINNED is set.
1304  *
1305  * See add_timer() for further details.
1306  */
add_timer_local(struct timer_list * timer)1307 void add_timer_local(struct timer_list *timer)
1308 {
1309 	if (WARN_ON_ONCE(timer_pending(timer)))
1310 		return;
1311 	timer->flags |= TIMER_PINNED;
1312 	__mod_timer(timer, timer->expires, MOD_TIMER_NOTPENDING);
1313 }
1314 EXPORT_SYMBOL(add_timer_local);
1315 
1316 /**
1317  * add_timer_global() - Start a timer without TIMER_PINNED flag set
1318  * @timer:	The timer to be started
1319  *
1320  * Same as add_timer() except that the timer flag TIMER_PINNED is unset.
1321  *
1322  * See add_timer() for further details.
1323  */
add_timer_global(struct timer_list * timer)1324 void add_timer_global(struct timer_list *timer)
1325 {
1326 	if (WARN_ON_ONCE(timer_pending(timer)))
1327 		return;
1328 	timer->flags &= ~TIMER_PINNED;
1329 	__mod_timer(timer, timer->expires, MOD_TIMER_NOTPENDING);
1330 }
1331 EXPORT_SYMBOL(add_timer_global);
1332 
1333 /**
1334  * add_timer_on - Start a timer on a particular CPU
1335  * @timer:	The timer to be started
1336  * @cpu:	The CPU to start it on
1337  *
1338  * Same as add_timer() except that it starts the timer on the given CPU and
1339  * the TIMER_PINNED flag is set. When timer shouldn't be a pinned timer in
1340  * the next round, add_timer_global() should be used instead as it unsets
1341  * the TIMER_PINNED flag.
1342  *
1343  * See add_timer() for further details.
1344  */
add_timer_on(struct timer_list * timer,int cpu)1345 void add_timer_on(struct timer_list *timer, int cpu)
1346 {
1347 	struct timer_base *new_base, *base;
1348 	unsigned long flags;
1349 
1350 	debug_assert_init(timer);
1351 
1352 	if (WARN_ON_ONCE(timer_pending(timer)))
1353 		return;
1354 
1355 	/* Make sure timer flags have TIMER_PINNED flag set */
1356 	timer->flags |= TIMER_PINNED;
1357 
1358 	new_base = get_timer_cpu_base(timer->flags, cpu);
1359 
1360 	/*
1361 	 * If @timer was on a different CPU, it should be migrated with the
1362 	 * old base locked to prevent other operations proceeding with the
1363 	 * wrong base locked.  See lock_timer_base().
1364 	 */
1365 	base = lock_timer_base(timer, &flags);
1366 	/*
1367 	 * Has @timer been shutdown? This needs to be evaluated while
1368 	 * holding base lock to prevent a race against the shutdown code.
1369 	 */
1370 	if (!timer->function)
1371 		goto out_unlock;
1372 
1373 	if (base != new_base) {
1374 		timer->flags |= TIMER_MIGRATING;
1375 
1376 		raw_spin_unlock(&base->lock);
1377 		base = new_base;
1378 		raw_spin_lock(&base->lock);
1379 		WRITE_ONCE(timer->flags,
1380 			   (timer->flags & ~TIMER_BASEMASK) | cpu);
1381 	}
1382 	forward_timer_base(base);
1383 
1384 	debug_timer_activate(timer);
1385 	internal_add_timer(base, timer);
1386 out_unlock:
1387 	raw_spin_unlock_irqrestore(&base->lock, flags);
1388 }
1389 EXPORT_SYMBOL_GPL(add_timer_on);
1390 
1391 /**
1392  * __timer_delete - Internal function: Deactivate a timer
1393  * @timer:	The timer to be deactivated
1394  * @shutdown:	If true, this indicates that the timer is about to be
1395  *		shutdown permanently.
1396  *
1397  * If @shutdown is true then @timer->function is set to NULL under the
1398  * timer base lock which prevents further rearming of the time. In that
1399  * case any attempt to rearm @timer after this function returns will be
1400  * silently ignored.
1401  *
1402  * Return:
1403  * * %0 - The timer was not pending
1404  * * %1 - The timer was pending and deactivated
1405  */
__timer_delete(struct timer_list * timer,bool shutdown)1406 static int __timer_delete(struct timer_list *timer, bool shutdown)
1407 {
1408 	struct timer_base *base;
1409 	unsigned long flags;
1410 	int ret = 0;
1411 
1412 	debug_assert_init(timer);
1413 
1414 	/*
1415 	 * If @shutdown is set then the lock has to be taken whether the
1416 	 * timer is pending or not to protect against a concurrent rearm
1417 	 * which might hit between the lockless pending check and the lock
1418 	 * acquisition. By taking the lock it is ensured that such a newly
1419 	 * enqueued timer is dequeued and cannot end up with
1420 	 * timer->function == NULL in the expiry code.
1421 	 *
1422 	 * If timer->function is currently executed, then this makes sure
1423 	 * that the callback cannot requeue the timer.
1424 	 */
1425 	if (timer_pending(timer) || shutdown) {
1426 		base = lock_timer_base(timer, &flags);
1427 		ret = detach_if_pending(timer, base, true);
1428 		if (shutdown)
1429 			timer->function = NULL;
1430 		raw_spin_unlock_irqrestore(&base->lock, flags);
1431 	}
1432 
1433 	return ret;
1434 }
1435 
1436 /**
1437  * timer_delete - Deactivate a timer
1438  * @timer:	The timer to be deactivated
1439  *
1440  * The function only deactivates a pending timer, but contrary to
1441  * timer_delete_sync() it does not take into account whether the timer's
1442  * callback function is concurrently executed on a different CPU or not.
1443  * It neither prevents rearming of the timer.  If @timer can be rearmed
1444  * concurrently then the return value of this function is meaningless.
1445  *
1446  * Return:
1447  * * %0 - The timer was not pending
1448  * * %1 - The timer was pending and deactivated
1449  */
timer_delete(struct timer_list * timer)1450 int timer_delete(struct timer_list *timer)
1451 {
1452 	return __timer_delete(timer, false);
1453 }
1454 EXPORT_SYMBOL(timer_delete);
1455 
1456 /**
1457  * timer_shutdown - Deactivate a timer and prevent rearming
1458  * @timer:	The timer to be deactivated
1459  *
1460  * The function does not wait for an eventually running timer callback on a
1461  * different CPU but it prevents rearming of the timer. Any attempt to arm
1462  * @timer after this function returns will be silently ignored.
1463  *
1464  * This function is useful for teardown code and should only be used when
1465  * timer_shutdown_sync() cannot be invoked due to locking or context constraints.
1466  *
1467  * Return:
1468  * * %0 - The timer was not pending
1469  * * %1 - The timer was pending
1470  */
timer_shutdown(struct timer_list * timer)1471 int timer_shutdown(struct timer_list *timer)
1472 {
1473 	return __timer_delete(timer, true);
1474 }
1475 EXPORT_SYMBOL_GPL(timer_shutdown);
1476 
1477 /**
1478  * __try_to_del_timer_sync - Internal function: Try to deactivate a timer
1479  * @timer:	Timer to deactivate
1480  * @shutdown:	If true, this indicates that the timer is about to be
1481  *		shutdown permanently.
1482  *
1483  * If @shutdown is true then @timer->function is set to NULL under the
1484  * timer base lock which prevents further rearming of the timer. Any
1485  * attempt to rearm @timer after this function returns will be silently
1486  * ignored.
1487  *
1488  * This function cannot guarantee that the timer cannot be rearmed
1489  * right after dropping the base lock if @shutdown is false. That
1490  * needs to be prevented by the calling code if necessary.
1491  *
1492  * Return:
1493  * * %0  - The timer was not pending
1494  * * %1  - The timer was pending and deactivated
1495  * * %-1 - The timer callback function is running on a different CPU
1496  */
__try_to_del_timer_sync(struct timer_list * timer,bool shutdown)1497 static int __try_to_del_timer_sync(struct timer_list *timer, bool shutdown)
1498 {
1499 	struct timer_base *base;
1500 	unsigned long flags;
1501 	int ret = -1;
1502 
1503 	debug_assert_init(timer);
1504 
1505 	base = lock_timer_base(timer, &flags);
1506 
1507 	if (base->running_timer != timer)
1508 		ret = detach_if_pending(timer, base, true);
1509 	if (shutdown)
1510 		timer->function = NULL;
1511 
1512 	raw_spin_unlock_irqrestore(&base->lock, flags);
1513 
1514 	return ret;
1515 }
1516 
1517 /**
1518  * try_to_del_timer_sync - Try to deactivate a timer
1519  * @timer:	Timer to deactivate
1520  *
1521  * This function tries to deactivate a timer. On success the timer is not
1522  * queued and the timer callback function is not running on any CPU.
1523  *
1524  * This function does not guarantee that the timer cannot be rearmed right
1525  * after dropping the base lock. That needs to be prevented by the calling
1526  * code if necessary.
1527  *
1528  * Return:
1529  * * %0  - The timer was not pending
1530  * * %1  - The timer was pending and deactivated
1531  * * %-1 - The timer callback function is running on a different CPU
1532  */
try_to_del_timer_sync(struct timer_list * timer)1533 int try_to_del_timer_sync(struct timer_list *timer)
1534 {
1535 	return __try_to_del_timer_sync(timer, false);
1536 }
1537 EXPORT_SYMBOL(try_to_del_timer_sync);
1538 
1539 #ifdef CONFIG_PREEMPT_RT
timer_base_init_expiry_lock(struct timer_base * base)1540 static __init void timer_base_init_expiry_lock(struct timer_base *base)
1541 {
1542 	spin_lock_init(&base->expiry_lock);
1543 }
1544 
timer_base_lock_expiry(struct timer_base * base)1545 static inline void timer_base_lock_expiry(struct timer_base *base)
1546 {
1547 	spin_lock(&base->expiry_lock);
1548 }
1549 
timer_base_unlock_expiry(struct timer_base * base)1550 static inline void timer_base_unlock_expiry(struct timer_base *base)
1551 {
1552 	spin_unlock(&base->expiry_lock);
1553 }
1554 
1555 /*
1556  * The counterpart to del_timer_wait_running().
1557  *
1558  * If there is a waiter for base->expiry_lock, then it was waiting for the
1559  * timer callback to finish. Drop expiry_lock and reacquire it. That allows
1560  * the waiter to acquire the lock and make progress.
1561  */
timer_sync_wait_running(struct timer_base * base)1562 static void timer_sync_wait_running(struct timer_base *base)
1563 	__releases(&base->lock) __releases(&base->expiry_lock)
1564 	__acquires(&base->expiry_lock) __acquires(&base->lock)
1565 {
1566 	if (atomic_read(&base->timer_waiters)) {
1567 		raw_spin_unlock_irq(&base->lock);
1568 		spin_unlock(&base->expiry_lock);
1569 		spin_lock(&base->expiry_lock);
1570 		raw_spin_lock_irq(&base->lock);
1571 	}
1572 }
1573 
1574 /*
1575  * This function is called on PREEMPT_RT kernels when the fast path
1576  * deletion of a timer failed because the timer callback function was
1577  * running.
1578  *
1579  * This prevents priority inversion, if the softirq thread on a remote CPU
1580  * got preempted, and it prevents a life lock when the task which tries to
1581  * delete a timer preempted the softirq thread running the timer callback
1582  * function.
1583  */
del_timer_wait_running(struct timer_list * timer)1584 static void del_timer_wait_running(struct timer_list *timer)
1585 {
1586 	u32 tf;
1587 
1588 	tf = READ_ONCE(timer->flags);
1589 	if (!(tf & (TIMER_MIGRATING | TIMER_IRQSAFE))) {
1590 		struct timer_base *base = get_timer_base(tf);
1591 
1592 		/*
1593 		 * Mark the base as contended and grab the expiry lock,
1594 		 * which is held by the softirq across the timer
1595 		 * callback. Drop the lock immediately so the softirq can
1596 		 * expire the next timer. In theory the timer could already
1597 		 * be running again, but that's more than unlikely and just
1598 		 * causes another wait loop.
1599 		 */
1600 		atomic_inc(&base->timer_waiters);
1601 		spin_lock_bh(&base->expiry_lock);
1602 		atomic_dec(&base->timer_waiters);
1603 		spin_unlock_bh(&base->expiry_lock);
1604 	}
1605 }
1606 #else
timer_base_init_expiry_lock(struct timer_base * base)1607 static inline void timer_base_init_expiry_lock(struct timer_base *base) { }
timer_base_lock_expiry(struct timer_base * base)1608 static inline void timer_base_lock_expiry(struct timer_base *base) { }
timer_base_unlock_expiry(struct timer_base * base)1609 static inline void timer_base_unlock_expiry(struct timer_base *base) { }
timer_sync_wait_running(struct timer_base * base)1610 static inline void timer_sync_wait_running(struct timer_base *base) { }
del_timer_wait_running(struct timer_list * timer)1611 static inline void del_timer_wait_running(struct timer_list *timer) { }
1612 #endif
1613 
1614 /**
1615  * __timer_delete_sync - Internal function: Deactivate a timer and wait
1616  *			 for the handler to finish.
1617  * @timer:	The timer to be deactivated
1618  * @shutdown:	If true, @timer->function will be set to NULL under the
1619  *		timer base lock which prevents rearming of @timer
1620  *
1621  * If @shutdown is not set the timer can be rearmed later. If the timer can
1622  * be rearmed concurrently, i.e. after dropping the base lock then the
1623  * return value is meaningless.
1624  *
1625  * If @shutdown is set then @timer->function is set to NULL under timer
1626  * base lock which prevents rearming of the timer. Any attempt to rearm
1627  * a shutdown timer is silently ignored.
1628  *
1629  * If the timer should be reused after shutdown it has to be initialized
1630  * again.
1631  *
1632  * Return:
1633  * * %0	- The timer was not pending
1634  * * %1	- The timer was pending and deactivated
1635  */
__timer_delete_sync(struct timer_list * timer,bool shutdown)1636 static int __timer_delete_sync(struct timer_list *timer, bool shutdown)
1637 {
1638 	int ret;
1639 
1640 #ifdef CONFIG_LOCKDEP
1641 	unsigned long flags;
1642 
1643 	/*
1644 	 * If lockdep gives a backtrace here, please reference
1645 	 * the synchronization rules above.
1646 	 */
1647 	local_irq_save(flags);
1648 	lock_map_acquire(&timer->lockdep_map);
1649 	lock_map_release(&timer->lockdep_map);
1650 	local_irq_restore(flags);
1651 #endif
1652 	/*
1653 	 * don't use it in hardirq context, because it
1654 	 * could lead to deadlock.
1655 	 */
1656 	WARN_ON(in_hardirq() && !(timer->flags & TIMER_IRQSAFE));
1657 
1658 	/*
1659 	 * Must be able to sleep on PREEMPT_RT because of the slowpath in
1660 	 * del_timer_wait_running().
1661 	 */
1662 	if (IS_ENABLED(CONFIG_PREEMPT_RT) && !(timer->flags & TIMER_IRQSAFE))
1663 		lockdep_assert_preemption_enabled();
1664 
1665 	do {
1666 		ret = __try_to_del_timer_sync(timer, shutdown);
1667 
1668 		if (unlikely(ret < 0)) {
1669 			del_timer_wait_running(timer);
1670 			cpu_relax();
1671 		}
1672 	} while (ret < 0);
1673 
1674 	return ret;
1675 }
1676 
1677 /**
1678  * timer_delete_sync - Deactivate a timer and wait for the handler to finish.
1679  * @timer:	The timer to be deactivated
1680  *
1681  * Synchronization rules: Callers must prevent restarting of the timer,
1682  * otherwise this function is meaningless. It must not be called from
1683  * interrupt contexts unless the timer is an irqsafe one. The caller must
1684  * not hold locks which would prevent completion of the timer's callback
1685  * function. The timer's handler must not call add_timer_on(). Upon exit
1686  * the timer is not queued and the handler is not running on any CPU.
1687  *
1688  * For !irqsafe timers, the caller must not hold locks that are held in
1689  * interrupt context. Even if the lock has nothing to do with the timer in
1690  * question.  Here's why::
1691  *
1692  *    CPU0                             CPU1
1693  *    ----                             ----
1694  *                                     <SOFTIRQ>
1695  *                                       call_timer_fn();
1696  *                                       base->running_timer = mytimer;
1697  *    spin_lock_irq(somelock);
1698  *                                     <IRQ>
1699  *                                        spin_lock(somelock);
1700  *    timer_delete_sync(mytimer);
1701  *    while (base->running_timer == mytimer);
1702  *
1703  * Now timer_delete_sync() will never return and never release somelock.
1704  * The interrupt on the other CPU is waiting to grab somelock but it has
1705  * interrupted the softirq that CPU0 is waiting to finish.
1706  *
1707  * This function cannot guarantee that the timer is not rearmed again by
1708  * some concurrent or preempting code, right after it dropped the base
1709  * lock. If there is the possibility of a concurrent rearm then the return
1710  * value of the function is meaningless.
1711  *
1712  * If such a guarantee is needed, e.g. for teardown situations then use
1713  * timer_shutdown_sync() instead.
1714  *
1715  * Return:
1716  * * %0	- The timer was not pending
1717  * * %1	- The timer was pending and deactivated
1718  */
timer_delete_sync(struct timer_list * timer)1719 int timer_delete_sync(struct timer_list *timer)
1720 {
1721 	return __timer_delete_sync(timer, false);
1722 }
1723 EXPORT_SYMBOL(timer_delete_sync);
1724 
1725 /**
1726  * timer_shutdown_sync - Shutdown a timer and prevent rearming
1727  * @timer: The timer to be shutdown
1728  *
1729  * When the function returns it is guaranteed that:
1730  *   - @timer is not queued
1731  *   - The callback function of @timer is not running
1732  *   - @timer cannot be enqueued again. Any attempt to rearm
1733  *     @timer is silently ignored.
1734  *
1735  * See timer_delete_sync() for synchronization rules.
1736  *
1737  * This function is useful for final teardown of an infrastructure where
1738  * the timer is subject to a circular dependency problem.
1739  *
1740  * A common pattern for this is a timer and a workqueue where the timer can
1741  * schedule work and work can arm the timer. On shutdown the workqueue must
1742  * be destroyed and the timer must be prevented from rearming. Unless the
1743  * code has conditionals like 'if (mything->in_shutdown)' to prevent that
1744  * there is no way to get this correct with timer_delete_sync().
1745  *
1746  * timer_shutdown_sync() is solving the problem. The correct ordering of
1747  * calls in this case is:
1748  *
1749  *	timer_shutdown_sync(&mything->timer);
1750  *	workqueue_destroy(&mything->workqueue);
1751  *
1752  * After this 'mything' can be safely freed.
1753  *
1754  * This obviously implies that the timer is not required to be functional
1755  * for the rest of the shutdown operation.
1756  *
1757  * Return:
1758  * * %0 - The timer was not pending
1759  * * %1 - The timer was pending
1760  */
timer_shutdown_sync(struct timer_list * timer)1761 int timer_shutdown_sync(struct timer_list *timer)
1762 {
1763 	return __timer_delete_sync(timer, true);
1764 }
1765 EXPORT_SYMBOL_GPL(timer_shutdown_sync);
1766 
call_timer_fn(struct timer_list * timer,void (* fn)(struct timer_list *),unsigned long baseclk)1767 static void call_timer_fn(struct timer_list *timer,
1768 			  void (*fn)(struct timer_list *),
1769 			  unsigned long baseclk)
1770 {
1771 	int count = preempt_count();
1772 
1773 #ifdef CONFIG_LOCKDEP
1774 	/*
1775 	 * It is permissible to free the timer from inside the
1776 	 * function that is called from it, this we need to take into
1777 	 * account for lockdep too. To avoid bogus "held lock freed"
1778 	 * warnings as well as problems when looking into
1779 	 * timer->lockdep_map, make a copy and use that here.
1780 	 */
1781 	struct lockdep_map lockdep_map;
1782 
1783 	lockdep_copy_map(&lockdep_map, &timer->lockdep_map);
1784 #endif
1785 	/*
1786 	 * Couple the lock chain with the lock chain at
1787 	 * timer_delete_sync() by acquiring the lock_map around the fn()
1788 	 * call here and in timer_delete_sync().
1789 	 */
1790 	lock_map_acquire(&lockdep_map);
1791 
1792 	trace_timer_expire_entry(timer, baseclk);
1793 	fn(timer);
1794 	trace_timer_expire_exit(timer);
1795 
1796 	lock_map_release(&lockdep_map);
1797 
1798 	if (count != preempt_count()) {
1799 		WARN_ONCE(1, "timer: %pS preempt leak: %08x -> %08x\n",
1800 			  fn, count, preempt_count());
1801 		/*
1802 		 * Restore the preempt count. That gives us a decent
1803 		 * chance to survive and extract information. If the
1804 		 * callback kept a lock held, bad luck, but not worse
1805 		 * than the BUG() we had.
1806 		 */
1807 		preempt_count_set(count);
1808 	}
1809 }
1810 
expire_timers(struct timer_base * base,struct hlist_head * head)1811 static void expire_timers(struct timer_base *base, struct hlist_head *head)
1812 {
1813 	/*
1814 	 * This value is required only for tracing. base->clk was
1815 	 * incremented directly before expire_timers was called. But expiry
1816 	 * is related to the old base->clk value.
1817 	 */
1818 	unsigned long baseclk = base->clk - 1;
1819 
1820 	while (!hlist_empty(head)) {
1821 		struct timer_list *timer;
1822 		void (*fn)(struct timer_list *);
1823 
1824 		timer = hlist_entry(head->first, struct timer_list, entry);
1825 
1826 		base->running_timer = timer;
1827 		detach_timer(timer, true);
1828 
1829 		fn = timer->function;
1830 
1831 		if (WARN_ON_ONCE(!fn)) {
1832 			/* Should never happen. Emphasis on should! */
1833 			base->running_timer = NULL;
1834 			continue;
1835 		}
1836 
1837 		if (timer->flags & TIMER_IRQSAFE) {
1838 			raw_spin_unlock(&base->lock);
1839 			call_timer_fn(timer, fn, baseclk);
1840 			raw_spin_lock(&base->lock);
1841 			base->running_timer = NULL;
1842 		} else {
1843 			raw_spin_unlock_irq(&base->lock);
1844 			call_timer_fn(timer, fn, baseclk);
1845 			raw_spin_lock_irq(&base->lock);
1846 			base->running_timer = NULL;
1847 			timer_sync_wait_running(base);
1848 		}
1849 	}
1850 }
1851 
collect_expired_timers(struct timer_base * base,struct hlist_head * heads)1852 static int collect_expired_timers(struct timer_base *base,
1853 				  struct hlist_head *heads)
1854 {
1855 	unsigned long clk = base->clk = base->next_expiry;
1856 	struct hlist_head *vec;
1857 	int i, levels = 0;
1858 	unsigned int idx;
1859 
1860 	for (i = 0; i < LVL_DEPTH; i++) {
1861 		idx = (clk & LVL_MASK) + i * LVL_SIZE;
1862 
1863 		if (__test_and_clear_bit(idx, base->pending_map)) {
1864 			vec = base->vectors + idx;
1865 			hlist_move_list(vec, heads++);
1866 			levels++;
1867 		}
1868 		/* Is it time to look at the next level? */
1869 		if (clk & LVL_CLK_MASK)
1870 			break;
1871 		/* Shift clock for the next level granularity */
1872 		clk >>= LVL_CLK_SHIFT;
1873 	}
1874 	return levels;
1875 }
1876 
1877 /*
1878  * Find the next pending bucket of a level. Search from level start (@offset)
1879  * + @clk upwards and if nothing there, search from start of the level
1880  * (@offset) up to @offset + clk.
1881  */
next_pending_bucket(struct timer_base * base,unsigned offset,unsigned clk)1882 static int next_pending_bucket(struct timer_base *base, unsigned offset,
1883 			       unsigned clk)
1884 {
1885 	unsigned pos, start = offset + clk;
1886 	unsigned end = offset + LVL_SIZE;
1887 
1888 	pos = find_next_bit(base->pending_map, end, start);
1889 	if (pos < end)
1890 		return pos - start;
1891 
1892 	pos = find_next_bit(base->pending_map, start, offset);
1893 	return pos < start ? pos + LVL_SIZE - start : -1;
1894 }
1895 
1896 /*
1897  * Search the first expiring timer in the various clock levels. Caller must
1898  * hold base->lock.
1899  *
1900  * Store next expiry time in base->next_expiry.
1901  */
timer_recalc_next_expiry(struct timer_base * base)1902 static void timer_recalc_next_expiry(struct timer_base *base)
1903 {
1904 	unsigned long clk, next, adj;
1905 	unsigned lvl, offset = 0;
1906 
1907 	next = base->clk + NEXT_TIMER_MAX_DELTA;
1908 	clk = base->clk;
1909 	for (lvl = 0; lvl < LVL_DEPTH; lvl++, offset += LVL_SIZE) {
1910 		int pos = next_pending_bucket(base, offset, clk & LVL_MASK);
1911 		unsigned long lvl_clk = clk & LVL_CLK_MASK;
1912 
1913 		if (pos >= 0) {
1914 			unsigned long tmp = clk + (unsigned long) pos;
1915 
1916 			tmp <<= LVL_SHIFT(lvl);
1917 			if (time_before(tmp, next))
1918 				next = tmp;
1919 
1920 			/*
1921 			 * If the next expiration happens before we reach
1922 			 * the next level, no need to check further.
1923 			 */
1924 			if (pos <= ((LVL_CLK_DIV - lvl_clk) & LVL_CLK_MASK))
1925 				break;
1926 		}
1927 		/*
1928 		 * Clock for the next level. If the current level clock lower
1929 		 * bits are zero, we look at the next level as is. If not we
1930 		 * need to advance it by one because that's going to be the
1931 		 * next expiring bucket in that level. base->clk is the next
1932 		 * expiring jiffy. So in case of:
1933 		 *
1934 		 * LVL5 LVL4 LVL3 LVL2 LVL1 LVL0
1935 		 *  0    0    0    0    0    0
1936 		 *
1937 		 * we have to look at all levels @index 0. With
1938 		 *
1939 		 * LVL5 LVL4 LVL3 LVL2 LVL1 LVL0
1940 		 *  0    0    0    0    0    2
1941 		 *
1942 		 * LVL0 has the next expiring bucket @index 2. The upper
1943 		 * levels have the next expiring bucket @index 1.
1944 		 *
1945 		 * In case that the propagation wraps the next level the same
1946 		 * rules apply:
1947 		 *
1948 		 * LVL5 LVL4 LVL3 LVL2 LVL1 LVL0
1949 		 *  0    0    0    0    F    2
1950 		 *
1951 		 * So after looking at LVL0 we get:
1952 		 *
1953 		 * LVL5 LVL4 LVL3 LVL2 LVL1
1954 		 *  0    0    0    1    0
1955 		 *
1956 		 * So no propagation from LVL1 to LVL2 because that happened
1957 		 * with the add already, but then we need to propagate further
1958 		 * from LVL2 to LVL3.
1959 		 *
1960 		 * So the simple check whether the lower bits of the current
1961 		 * level are 0 or not is sufficient for all cases.
1962 		 */
1963 		adj = lvl_clk ? 1 : 0;
1964 		clk >>= LVL_CLK_SHIFT;
1965 		clk += adj;
1966 	}
1967 
1968 	WRITE_ONCE(base->next_expiry, next);
1969 	base->next_expiry_recalc = false;
1970 	base->timers_pending = !(next == base->clk + NEXT_TIMER_MAX_DELTA);
1971 }
1972 
1973 #ifdef CONFIG_NO_HZ_COMMON
1974 /*
1975  * Check, if the next hrtimer event is before the next timer wheel
1976  * event:
1977  */
cmp_next_hrtimer_event(u64 basem,u64 expires)1978 static u64 cmp_next_hrtimer_event(u64 basem, u64 expires)
1979 {
1980 	u64 nextevt = hrtimer_get_next_event();
1981 
1982 	/*
1983 	 * If high resolution timers are enabled
1984 	 * hrtimer_get_next_event() returns KTIME_MAX.
1985 	 */
1986 	if (expires <= nextevt)
1987 		return expires;
1988 
1989 	/*
1990 	 * If the next timer is already expired, return the tick base
1991 	 * time so the tick is fired immediately.
1992 	 */
1993 	if (nextevt <= basem)
1994 		return basem;
1995 
1996 	/*
1997 	 * Round up to the next jiffy. High resolution timers are
1998 	 * off, so the hrtimers are expired in the tick and we need to
1999 	 * make sure that this tick really expires the timer to avoid
2000 	 * a ping pong of the nohz stop code.
2001 	 *
2002 	 * Use DIV_ROUND_UP_ULL to prevent gcc calling __divdi3
2003 	 */
2004 	return DIV_ROUND_UP_ULL(nextevt, TICK_NSEC) * TICK_NSEC;
2005 }
2006 
next_timer_interrupt(struct timer_base * base,unsigned long basej)2007 static unsigned long next_timer_interrupt(struct timer_base *base,
2008 					  unsigned long basej)
2009 {
2010 	if (base->next_expiry_recalc)
2011 		timer_recalc_next_expiry(base);
2012 
2013 	/*
2014 	 * Move next_expiry for the empty base into the future to prevent an
2015 	 * unnecessary raise of the timer softirq when the next_expiry value
2016 	 * will be reached even if there is no timer pending.
2017 	 *
2018 	 * This update is also required to make timer_base::next_expiry values
2019 	 * easy comparable to find out which base holds the first pending timer.
2020 	 */
2021 	if (!base->timers_pending)
2022 		WRITE_ONCE(base->next_expiry, basej + NEXT_TIMER_MAX_DELTA);
2023 
2024 	return base->next_expiry;
2025 }
2026 
fetch_next_timer_interrupt(unsigned long basej,u64 basem,struct timer_base * base_local,struct timer_base * base_global,struct timer_events * tevt)2027 static unsigned long fetch_next_timer_interrupt(unsigned long basej, u64 basem,
2028 						struct timer_base *base_local,
2029 						struct timer_base *base_global,
2030 						struct timer_events *tevt)
2031 {
2032 	unsigned long nextevt, nextevt_local, nextevt_global;
2033 	bool local_first;
2034 
2035 	nextevt_local = next_timer_interrupt(base_local, basej);
2036 	nextevt_global = next_timer_interrupt(base_global, basej);
2037 
2038 	local_first = time_before_eq(nextevt_local, nextevt_global);
2039 
2040 	nextevt = local_first ? nextevt_local : nextevt_global;
2041 
2042 	/*
2043 	 * If the @nextevt is at max. one tick away, use @nextevt and store
2044 	 * it in the local expiry value. The next global event is irrelevant in
2045 	 * this case and can be left as KTIME_MAX.
2046 	 */
2047 	if (time_before_eq(nextevt, basej + 1)) {
2048 		/* If we missed a tick already, force 0 delta */
2049 		if (time_before(nextevt, basej))
2050 			nextevt = basej;
2051 		tevt->local = basem + (u64)(nextevt - basej) * TICK_NSEC;
2052 
2053 		/*
2054 		 * This is required for the remote check only but it doesn't
2055 		 * hurt, when it is done for both call sites:
2056 		 *
2057 		 * * The remote callers will only take care of the global timers
2058 		 *   as local timers will be handled by CPU itself. When not
2059 		 *   updating tevt->global with the already missed first global
2060 		 *   timer, it is possible that it will be missed completely.
2061 		 *
2062 		 * * The local callers will ignore the tevt->global anyway, when
2063 		 *   nextevt is max. one tick away.
2064 		 */
2065 		if (!local_first)
2066 			tevt->global = tevt->local;
2067 		return nextevt;
2068 	}
2069 
2070 	/*
2071 	 * Update tevt.* values:
2072 	 *
2073 	 * If the local queue expires first, then the global event can be
2074 	 * ignored. If the global queue is empty, nothing to do either.
2075 	 */
2076 	if (!local_first && base_global->timers_pending)
2077 		tevt->global = basem + (u64)(nextevt_global - basej) * TICK_NSEC;
2078 
2079 	if (base_local->timers_pending)
2080 		tevt->local = basem + (u64)(nextevt_local - basej) * TICK_NSEC;
2081 
2082 	return nextevt;
2083 }
2084 
2085 # ifdef CONFIG_SMP
2086 /**
2087  * fetch_next_timer_interrupt_remote() - Store next timers into @tevt
2088  * @basej:	base time jiffies
2089  * @basem:	base time clock monotonic
2090  * @tevt:	Pointer to the storage for the expiry values
2091  * @cpu:	Remote CPU
2092  *
2093  * Stores the next pending local and global timer expiry values in the
2094  * struct pointed to by @tevt. If a queue is empty the corresponding
2095  * field is set to KTIME_MAX. If local event expires before global
2096  * event, global event is set to KTIME_MAX as well.
2097  *
2098  * Caller needs to make sure timer base locks are held (use
2099  * timer_lock_remote_bases() for this purpose).
2100  */
fetch_next_timer_interrupt_remote(unsigned long basej,u64 basem,struct timer_events * tevt,unsigned int cpu)2101 void fetch_next_timer_interrupt_remote(unsigned long basej, u64 basem,
2102 				       struct timer_events *tevt,
2103 				       unsigned int cpu)
2104 {
2105 	struct timer_base *base_local, *base_global;
2106 
2107 	/* Preset local / global events */
2108 	tevt->local = tevt->global = KTIME_MAX;
2109 
2110 	base_local = per_cpu_ptr(&timer_bases[BASE_LOCAL], cpu);
2111 	base_global = per_cpu_ptr(&timer_bases[BASE_GLOBAL], cpu);
2112 
2113 	lockdep_assert_held(&base_local->lock);
2114 	lockdep_assert_held(&base_global->lock);
2115 
2116 	fetch_next_timer_interrupt(basej, basem, base_local, base_global, tevt);
2117 }
2118 
2119 /**
2120  * timer_unlock_remote_bases - unlock timer bases of cpu
2121  * @cpu:	Remote CPU
2122  *
2123  * Unlocks the remote timer bases.
2124  */
timer_unlock_remote_bases(unsigned int cpu)2125 void timer_unlock_remote_bases(unsigned int cpu)
2126 	__releases(timer_bases[BASE_LOCAL]->lock)
2127 	__releases(timer_bases[BASE_GLOBAL]->lock)
2128 {
2129 	struct timer_base *base_local, *base_global;
2130 
2131 	base_local = per_cpu_ptr(&timer_bases[BASE_LOCAL], cpu);
2132 	base_global = per_cpu_ptr(&timer_bases[BASE_GLOBAL], cpu);
2133 
2134 	raw_spin_unlock(&base_global->lock);
2135 	raw_spin_unlock(&base_local->lock);
2136 }
2137 
2138 /**
2139  * timer_lock_remote_bases - lock timer bases of cpu
2140  * @cpu:	Remote CPU
2141  *
2142  * Locks the remote timer bases.
2143  */
timer_lock_remote_bases(unsigned int cpu)2144 void timer_lock_remote_bases(unsigned int cpu)
2145 	__acquires(timer_bases[BASE_LOCAL]->lock)
2146 	__acquires(timer_bases[BASE_GLOBAL]->lock)
2147 {
2148 	struct timer_base *base_local, *base_global;
2149 
2150 	base_local = per_cpu_ptr(&timer_bases[BASE_LOCAL], cpu);
2151 	base_global = per_cpu_ptr(&timer_bases[BASE_GLOBAL], cpu);
2152 
2153 	lockdep_assert_irqs_disabled();
2154 
2155 	raw_spin_lock(&base_local->lock);
2156 	raw_spin_lock_nested(&base_global->lock, SINGLE_DEPTH_NESTING);
2157 }
2158 
2159 /**
2160  * timer_base_is_idle() - Return whether timer base is set idle
2161  *
2162  * Returns value of local timer base is_idle value.
2163  */
timer_base_is_idle(void)2164 bool timer_base_is_idle(void)
2165 {
2166 	return __this_cpu_read(timer_bases[BASE_LOCAL].is_idle);
2167 }
2168 
2169 static void __run_timer_base(struct timer_base *base);
2170 
2171 /**
2172  * timer_expire_remote() - expire global timers of cpu
2173  * @cpu:	Remote CPU
2174  *
2175  * Expire timers of global base of remote CPU.
2176  */
timer_expire_remote(unsigned int cpu)2177 void timer_expire_remote(unsigned int cpu)
2178 {
2179 	struct timer_base *base = per_cpu_ptr(&timer_bases[BASE_GLOBAL], cpu);
2180 
2181 	__run_timer_base(base);
2182 }
2183 
timer_use_tmigr(unsigned long basej,u64 basem,unsigned long * nextevt,bool * tick_stop_path,bool timer_base_idle,struct timer_events * tevt)2184 static void timer_use_tmigr(unsigned long basej, u64 basem,
2185 			    unsigned long *nextevt, bool *tick_stop_path,
2186 			    bool timer_base_idle, struct timer_events *tevt)
2187 {
2188 	u64 next_tmigr;
2189 
2190 	if (timer_base_idle)
2191 		next_tmigr = tmigr_cpu_new_timer(tevt->global);
2192 	else if (tick_stop_path)
2193 		next_tmigr = tmigr_cpu_deactivate(tevt->global);
2194 	else
2195 		next_tmigr = tmigr_quick_check(tevt->global);
2196 
2197 	/*
2198 	 * If the CPU is the last going idle in timer migration hierarchy, make
2199 	 * sure the CPU will wake up in time to handle remote timers.
2200 	 * next_tmigr == KTIME_MAX if other CPUs are still active.
2201 	 */
2202 	if (next_tmigr < tevt->local) {
2203 		u64 tmp;
2204 
2205 		/* If we missed a tick already, force 0 delta */
2206 		if (next_tmigr < basem)
2207 			next_tmigr = basem;
2208 
2209 		tmp = div_u64(next_tmigr - basem, TICK_NSEC);
2210 
2211 		*nextevt = basej + (unsigned long)tmp;
2212 		tevt->local = next_tmigr;
2213 	}
2214 }
2215 # else
timer_use_tmigr(unsigned long basej,u64 basem,unsigned long * nextevt,bool * tick_stop_path,bool timer_base_idle,struct timer_events * tevt)2216 static void timer_use_tmigr(unsigned long basej, u64 basem,
2217 			    unsigned long *nextevt, bool *tick_stop_path,
2218 			    bool timer_base_idle, struct timer_events *tevt)
2219 {
2220 	/*
2221 	 * Make sure first event is written into tevt->local to not miss a
2222 	 * timer on !SMP systems.
2223 	 */
2224 	tevt->local = min_t(u64, tevt->local, tevt->global);
2225 }
2226 # endif /* CONFIG_SMP */
2227 
__get_next_timer_interrupt(unsigned long basej,u64 basem,bool * idle)2228 static inline u64 __get_next_timer_interrupt(unsigned long basej, u64 basem,
2229 					     bool *idle)
2230 {
2231 	struct timer_events tevt = { .local = KTIME_MAX, .global = KTIME_MAX };
2232 	struct timer_base *base_local, *base_global;
2233 	unsigned long nextevt;
2234 	bool idle_is_possible;
2235 
2236 	/*
2237 	 * When the CPU is offline, the tick is cancelled and nothing is supposed
2238 	 * to try to stop it.
2239 	 */
2240 	if (WARN_ON_ONCE(cpu_is_offline(smp_processor_id()))) {
2241 		if (idle)
2242 			*idle = true;
2243 		return tevt.local;
2244 	}
2245 
2246 	base_local = this_cpu_ptr(&timer_bases[BASE_LOCAL]);
2247 	base_global = this_cpu_ptr(&timer_bases[BASE_GLOBAL]);
2248 
2249 	raw_spin_lock(&base_local->lock);
2250 	raw_spin_lock_nested(&base_global->lock, SINGLE_DEPTH_NESTING);
2251 
2252 	nextevt = fetch_next_timer_interrupt(basej, basem, base_local,
2253 					     base_global, &tevt);
2254 
2255 	/*
2256 	 * If the next event is only one jiffy ahead there is no need to call
2257 	 * timer migration hierarchy related functions. The value for the next
2258 	 * global timer in @tevt struct equals then KTIME_MAX. This is also
2259 	 * true, when the timer base is idle.
2260 	 *
2261 	 * The proper timer migration hierarchy function depends on the callsite
2262 	 * and whether timer base is idle or not. @nextevt will be updated when
2263 	 * this CPU needs to handle the first timer migration hierarchy
2264 	 * event. See timer_use_tmigr() for detailed information.
2265 	 */
2266 	idle_is_possible = time_after(nextevt, basej + 1);
2267 	if (idle_is_possible)
2268 		timer_use_tmigr(basej, basem, &nextevt, idle,
2269 				base_local->is_idle, &tevt);
2270 
2271 	/*
2272 	 * We have a fresh next event. Check whether we can forward the
2273 	 * base.
2274 	 */
2275 	__forward_timer_base(base_local, basej);
2276 	__forward_timer_base(base_global, basej);
2277 
2278 	/*
2279 	 * Set base->is_idle only when caller is timer_base_try_to_set_idle()
2280 	 */
2281 	if (idle) {
2282 		/*
2283 		 * Bases are idle if the next event is more than a tick
2284 		 * away. Caution: @nextevt could have changed by enqueueing a
2285 		 * global timer into timer migration hierarchy. Therefore a new
2286 		 * check is required here.
2287 		 *
2288 		 * If the base is marked idle then any timer add operation must
2289 		 * forward the base clk itself to keep granularity small. This
2290 		 * idle logic is only maintained for the BASE_LOCAL and
2291 		 * BASE_GLOBAL base, deferrable timers may still see large
2292 		 * granularity skew (by design).
2293 		 */
2294 		if (!base_local->is_idle && time_after(nextevt, basej + 1)) {
2295 			base_local->is_idle = true;
2296 			/*
2297 			 * Global timers queued locally while running in a task
2298 			 * in nohz_full mode need a self-IPI to kick reprogramming
2299 			 * in IRQ tail.
2300 			 */
2301 			if (tick_nohz_full_cpu(base_local->cpu))
2302 				base_global->is_idle = true;
2303 			trace_timer_base_idle(true, base_local->cpu);
2304 		}
2305 		*idle = base_local->is_idle;
2306 
2307 		/*
2308 		 * When timer base is not set idle, undo the effect of
2309 		 * tmigr_cpu_deactivate() to prevent inconsistent states - active
2310 		 * timer base but inactive timer migration hierarchy.
2311 		 *
2312 		 * When timer base was already marked idle, nothing will be
2313 		 * changed here.
2314 		 */
2315 		if (!base_local->is_idle && idle_is_possible)
2316 			tmigr_cpu_activate();
2317 	}
2318 
2319 	raw_spin_unlock(&base_global->lock);
2320 	raw_spin_unlock(&base_local->lock);
2321 
2322 	return cmp_next_hrtimer_event(basem, tevt.local);
2323 }
2324 
2325 /**
2326  * get_next_timer_interrupt() - return the time (clock mono) of the next timer
2327  * @basej:	base time jiffies
2328  * @basem:	base time clock monotonic
2329  *
2330  * Returns the tick aligned clock monotonic time of the next pending timer or
2331  * KTIME_MAX if no timer is pending. If timer of global base was queued into
2332  * timer migration hierarchy, first global timer is not taken into account. If
2333  * it was the last CPU of timer migration hierarchy going idle, first global
2334  * event is taken into account.
2335  */
get_next_timer_interrupt(unsigned long basej,u64 basem)2336 u64 get_next_timer_interrupt(unsigned long basej, u64 basem)
2337 {
2338 	return __get_next_timer_interrupt(basej, basem, NULL);
2339 }
2340 
2341 /**
2342  * timer_base_try_to_set_idle() - Try to set the idle state of the timer bases
2343  * @basej:	base time jiffies
2344  * @basem:	base time clock monotonic
2345  * @idle:	pointer to store the value of timer_base->is_idle on return;
2346  *		*idle contains the information whether tick was already stopped
2347  *
2348  * Returns the tick aligned clock monotonic time of the next pending timer or
2349  * KTIME_MAX if no timer is pending. When tick was already stopped KTIME_MAX is
2350  * returned as well.
2351  */
timer_base_try_to_set_idle(unsigned long basej,u64 basem,bool * idle)2352 u64 timer_base_try_to_set_idle(unsigned long basej, u64 basem, bool *idle)
2353 {
2354 	if (*idle)
2355 		return KTIME_MAX;
2356 
2357 	return __get_next_timer_interrupt(basej, basem, idle);
2358 }
2359 
2360 /**
2361  * timer_clear_idle - Clear the idle state of the timer base
2362  *
2363  * Called with interrupts disabled
2364  */
timer_clear_idle(void)2365 void timer_clear_idle(void)
2366 {
2367 	/*
2368 	 * We do this unlocked. The worst outcome is a remote pinned timer
2369 	 * enqueue sending a pointless IPI, but taking the lock would just
2370 	 * make the window for sending the IPI a few instructions smaller
2371 	 * for the cost of taking the lock in the exit from idle
2372 	 * path. Required for BASE_LOCAL only.
2373 	 */
2374 	__this_cpu_write(timer_bases[BASE_LOCAL].is_idle, false);
2375 	if (tick_nohz_full_cpu(smp_processor_id()))
2376 		__this_cpu_write(timer_bases[BASE_GLOBAL].is_idle, false);
2377 	trace_timer_base_idle(false, smp_processor_id());
2378 
2379 	/* Activate without holding the timer_base->lock */
2380 	tmigr_cpu_activate();
2381 }
2382 #endif
2383 
2384 /**
2385  * __run_timers - run all expired timers (if any) on this CPU.
2386  * @base: the timer vector to be processed.
2387  */
__run_timers(struct timer_base * base)2388 static inline void __run_timers(struct timer_base *base)
2389 {
2390 	struct hlist_head heads[LVL_DEPTH];
2391 	int levels;
2392 
2393 	lockdep_assert_held(&base->lock);
2394 
2395 	if (base->running_timer)
2396 		return;
2397 
2398 	while (time_after_eq(jiffies, base->clk) &&
2399 	       time_after_eq(jiffies, base->next_expiry)) {
2400 		levels = collect_expired_timers(base, heads);
2401 		/*
2402 		 * The two possible reasons for not finding any expired
2403 		 * timer at this clk are that all matching timers have been
2404 		 * dequeued or no timer has been queued since
2405 		 * base::next_expiry was set to base::clk +
2406 		 * NEXT_TIMER_MAX_DELTA.
2407 		 */
2408 		WARN_ON_ONCE(!levels && !base->next_expiry_recalc
2409 			     && base->timers_pending);
2410 		/*
2411 		 * While executing timers, base->clk is set 1 offset ahead of
2412 		 * jiffies to avoid endless requeuing to current jiffies.
2413 		 */
2414 		base->clk++;
2415 		timer_recalc_next_expiry(base);
2416 
2417 		while (levels--)
2418 			expire_timers(base, heads + levels);
2419 	}
2420 }
2421 
__run_timer_base(struct timer_base * base)2422 static void __run_timer_base(struct timer_base *base)
2423 {
2424 	/* Can race against a remote CPU updating next_expiry under the lock */
2425 	if (time_before(jiffies, READ_ONCE(base->next_expiry)))
2426 		return;
2427 
2428 	timer_base_lock_expiry(base);
2429 	raw_spin_lock_irq(&base->lock);
2430 	__run_timers(base);
2431 	raw_spin_unlock_irq(&base->lock);
2432 	timer_base_unlock_expiry(base);
2433 }
2434 
run_timer_base(int index)2435 static void run_timer_base(int index)
2436 {
2437 	struct timer_base *base = this_cpu_ptr(&timer_bases[index]);
2438 
2439 	__run_timer_base(base);
2440 }
2441 
2442 /*
2443  * This function runs timers and the timer-tq in bottom half context.
2444  */
run_timer_softirq(void)2445 static __latent_entropy void run_timer_softirq(void)
2446 {
2447 	run_timer_base(BASE_LOCAL);
2448 	if (IS_ENABLED(CONFIG_NO_HZ_COMMON)) {
2449 		run_timer_base(BASE_GLOBAL);
2450 		run_timer_base(BASE_DEF);
2451 
2452 		if (is_timers_nohz_active())
2453 			tmigr_handle_remote();
2454 	}
2455 }
2456 
2457 /*
2458  * Called by the local, per-CPU timer interrupt on SMP.
2459  */
run_local_timers(void)2460 static void run_local_timers(void)
2461 {
2462 	struct timer_base *base = this_cpu_ptr(&timer_bases[BASE_LOCAL]);
2463 
2464 	hrtimer_run_queues();
2465 
2466 	for (int i = 0; i < NR_BASES; i++, base++) {
2467 		/*
2468 		 * Raise the softirq only if required.
2469 		 *
2470 		 * timer_base::next_expiry can be written by a remote CPU while
2471 		 * holding the lock. If this write happens at the same time than
2472 		 * the lockless local read, sanity checker could complain about
2473 		 * data corruption.
2474 		 *
2475 		 * There are two possible situations where
2476 		 * timer_base::next_expiry is written by a remote CPU:
2477 		 *
2478 		 * 1. Remote CPU expires global timers of this CPU and updates
2479 		 * timer_base::next_expiry of BASE_GLOBAL afterwards in
2480 		 * next_timer_interrupt() or timer_recalc_next_expiry(). The
2481 		 * worst outcome is a superfluous raise of the timer softirq
2482 		 * when the not yet updated value is read.
2483 		 *
2484 		 * 2. A new first pinned timer is enqueued by a remote CPU
2485 		 * and therefore timer_base::next_expiry of BASE_LOCAL is
2486 		 * updated. When this update is missed, this isn't a
2487 		 * problem, as an IPI is executed nevertheless when the CPU
2488 		 * was idle before. When the CPU wasn't idle but the update
2489 		 * is missed, then the timer would expire one jiffy late -
2490 		 * bad luck.
2491 		 *
2492 		 * Those unlikely corner cases where the worst outcome is only a
2493 		 * one jiffy delay or a superfluous raise of the softirq are
2494 		 * not that expensive as doing the check always while holding
2495 		 * the lock.
2496 		 *
2497 		 * Possible remote writers are using WRITE_ONCE(). Local reader
2498 		 * uses therefore READ_ONCE().
2499 		 */
2500 		if (time_after_eq(jiffies, READ_ONCE(base->next_expiry)) ||
2501 		    (i == BASE_DEF && tmigr_requires_handle_remote())) {
2502 			raise_timer_softirq(TIMER_SOFTIRQ);
2503 			return;
2504 		}
2505 	}
2506 }
2507 
2508 /*
2509  * Called from the timer interrupt handler to charge one tick to the current
2510  * process.  user_tick is 1 if the tick is user time, 0 for system.
2511  */
update_process_times(int user_tick)2512 void update_process_times(int user_tick)
2513 {
2514 	struct task_struct *p = current;
2515 
2516 	/* Note: this timer irq context must be accounted for as well. */
2517 	account_process_tick(p, user_tick);
2518 	run_local_timers();
2519 	rcu_sched_clock_irq(user_tick);
2520 #ifdef CONFIG_IRQ_WORK
2521 	if (in_irq())
2522 		irq_work_tick();
2523 #endif
2524 	sched_tick();
2525 	if (IS_ENABLED(CONFIG_POSIX_TIMERS))
2526 		run_posix_cpu_timers();
2527 }
2528 
2529 #ifdef CONFIG_HOTPLUG_CPU
migrate_timer_list(struct timer_base * new_base,struct hlist_head * head)2530 static void migrate_timer_list(struct timer_base *new_base, struct hlist_head *head)
2531 {
2532 	struct timer_list *timer;
2533 	int cpu = new_base->cpu;
2534 
2535 	while (!hlist_empty(head)) {
2536 		timer = hlist_entry(head->first, struct timer_list, entry);
2537 		detach_timer(timer, false);
2538 		timer->flags = (timer->flags & ~TIMER_BASEMASK) | cpu;
2539 		internal_add_timer(new_base, timer);
2540 	}
2541 }
2542 
timers_prepare_cpu(unsigned int cpu)2543 int timers_prepare_cpu(unsigned int cpu)
2544 {
2545 	struct timer_base *base;
2546 	int b;
2547 
2548 	for (b = 0; b < NR_BASES; b++) {
2549 		base = per_cpu_ptr(&timer_bases[b], cpu);
2550 		base->clk = jiffies;
2551 		base->next_expiry = base->clk + NEXT_TIMER_MAX_DELTA;
2552 		base->next_expiry_recalc = false;
2553 		base->timers_pending = false;
2554 		base->is_idle = false;
2555 	}
2556 	return 0;
2557 }
2558 
timers_dead_cpu(unsigned int cpu)2559 int timers_dead_cpu(unsigned int cpu)
2560 {
2561 	struct timer_base *old_base;
2562 	struct timer_base *new_base;
2563 	int b, i;
2564 
2565 	for (b = 0; b < NR_BASES; b++) {
2566 		old_base = per_cpu_ptr(&timer_bases[b], cpu);
2567 		new_base = get_cpu_ptr(&timer_bases[b]);
2568 		/*
2569 		 * The caller is globally serialized and nobody else
2570 		 * takes two locks at once, deadlock is not possible.
2571 		 */
2572 		raw_spin_lock_irq(&new_base->lock);
2573 		raw_spin_lock_nested(&old_base->lock, SINGLE_DEPTH_NESTING);
2574 
2575 		/*
2576 		 * The current CPUs base clock might be stale. Update it
2577 		 * before moving the timers over.
2578 		 */
2579 		forward_timer_base(new_base);
2580 
2581 		WARN_ON_ONCE(old_base->running_timer);
2582 		old_base->running_timer = NULL;
2583 
2584 		for (i = 0; i < WHEEL_SIZE; i++)
2585 			migrate_timer_list(new_base, old_base->vectors + i);
2586 
2587 		raw_spin_unlock(&old_base->lock);
2588 		raw_spin_unlock_irq(&new_base->lock);
2589 		put_cpu_ptr(&timer_bases);
2590 	}
2591 	return 0;
2592 }
2593 
2594 #endif /* CONFIG_HOTPLUG_CPU */
2595 
init_timer_cpu(int cpu)2596 static void __init init_timer_cpu(int cpu)
2597 {
2598 	struct timer_base *base;
2599 	int i;
2600 
2601 	for (i = 0; i < NR_BASES; i++) {
2602 		base = per_cpu_ptr(&timer_bases[i], cpu);
2603 		base->cpu = cpu;
2604 		raw_spin_lock_init(&base->lock);
2605 		base->clk = jiffies;
2606 		base->next_expiry = base->clk + NEXT_TIMER_MAX_DELTA;
2607 		timer_base_init_expiry_lock(base);
2608 	}
2609 }
2610 
init_timer_cpus(void)2611 static void __init init_timer_cpus(void)
2612 {
2613 	int cpu;
2614 
2615 	for_each_possible_cpu(cpu)
2616 		init_timer_cpu(cpu);
2617 }
2618 
init_timers(void)2619 void __init init_timers(void)
2620 {
2621 	init_timer_cpus();
2622 	posix_cputimers_init_work();
2623 	open_softirq(TIMER_SOFTIRQ, run_timer_softirq);
2624 }
2625