1 /* 2 * fs/timerfd.c 3 * 4 * Copyright (C) 2007 Davide Libenzi <davidel@xmailserver.org> 5 * 6 * 7 * Thanks to Thomas Gleixner for code reviews and useful comments. 8 * 9 */ 10 11 #include <linux/file.h> 12 #include <linux/poll.h> 13 #include <linux/init.h> 14 #include <linux/fs.h> 15 #include <linux/sched.h> 16 #include <linux/kernel.h> 17 #include <linux/slab.h> 18 #include <linux/list.h> 19 #include <linux/spinlock.h> 20 #include <linux/time.h> 21 #include <linux/hrtimer.h> 22 #include <linux/anon_inodes.h> 23 #include <linux/timerfd.h> 24 #include <linux/syscalls.h> 25 26 struct timerfd_ctx { 27 struct hrtimer tmr; 28 ktime_t tintv; 29 wait_queue_head_t wqh; 30 u64 ticks; 31 int expired; 32 int clockid; 33 }; 34 35 /* 36 * This gets called when the timer event triggers. We set the "expired" 37 * flag, but we do not re-arm the timer (in case it's necessary, 38 * tintv.tv64 != 0) until the timer is accessed. 39 */ 40 static enum hrtimer_restart timerfd_tmrproc(struct hrtimer *htmr) 41 { 42 struct timerfd_ctx *ctx = container_of(htmr, struct timerfd_ctx, tmr); 43 unsigned long flags; 44 45 spin_lock_irqsave(&ctx->wqh.lock, flags); 46 ctx->expired = 1; 47 ctx->ticks++; 48 wake_up_locked(&ctx->wqh); 49 spin_unlock_irqrestore(&ctx->wqh.lock, flags); 50 51 return HRTIMER_NORESTART; 52 } 53 54 static ktime_t timerfd_get_remaining(struct timerfd_ctx *ctx) 55 { 56 ktime_t remaining; 57 58 remaining = hrtimer_expires_remaining(&ctx->tmr); 59 return remaining.tv64 < 0 ? ktime_set(0, 0): remaining; 60 } 61 62 static void timerfd_setup(struct timerfd_ctx *ctx, int flags, 63 const struct itimerspec *ktmr) 64 { 65 enum hrtimer_mode htmode; 66 ktime_t texp; 67 68 htmode = (flags & TFD_TIMER_ABSTIME) ? 69 HRTIMER_MODE_ABS: HRTIMER_MODE_REL; 70 71 texp = timespec_to_ktime(ktmr->it_value); 72 ctx->expired = 0; 73 ctx->ticks = 0; 74 ctx->tintv = timespec_to_ktime(ktmr->it_interval); 75 hrtimer_init(&ctx->tmr, ctx->clockid, htmode); 76 hrtimer_set_expires(&ctx->tmr, texp); 77 ctx->tmr.function = timerfd_tmrproc; 78 if (texp.tv64 != 0) 79 hrtimer_start(&ctx->tmr, texp, htmode); 80 } 81 82 static int timerfd_release(struct inode *inode, struct file *file) 83 { 84 struct timerfd_ctx *ctx = file->private_data; 85 86 hrtimer_cancel(&ctx->tmr); 87 kfree(ctx); 88 return 0; 89 } 90 91 static unsigned int timerfd_poll(struct file *file, poll_table *wait) 92 { 93 struct timerfd_ctx *ctx = file->private_data; 94 unsigned int events = 0; 95 unsigned long flags; 96 97 poll_wait(file, &ctx->wqh, wait); 98 99 spin_lock_irqsave(&ctx->wqh.lock, flags); 100 if (ctx->ticks) 101 events |= POLLIN; 102 spin_unlock_irqrestore(&ctx->wqh.lock, flags); 103 104 return events; 105 } 106 107 static ssize_t timerfd_read(struct file *file, char __user *buf, size_t count, 108 loff_t *ppos) 109 { 110 struct timerfd_ctx *ctx = file->private_data; 111 ssize_t res; 112 u64 ticks = 0; 113 DECLARE_WAITQUEUE(wait, current); 114 115 if (count < sizeof(ticks)) 116 return -EINVAL; 117 spin_lock_irq(&ctx->wqh.lock); 118 res = -EAGAIN; 119 if (!ctx->ticks && !(file->f_flags & O_NONBLOCK)) { 120 __add_wait_queue(&ctx->wqh, &wait); 121 for (res = 0;;) { 122 set_current_state(TASK_INTERRUPTIBLE); 123 if (ctx->ticks) { 124 res = 0; 125 break; 126 } 127 if (signal_pending(current)) { 128 res = -ERESTARTSYS; 129 break; 130 } 131 spin_unlock_irq(&ctx->wqh.lock); 132 schedule(); 133 spin_lock_irq(&ctx->wqh.lock); 134 } 135 __remove_wait_queue(&ctx->wqh, &wait); 136 __set_current_state(TASK_RUNNING); 137 } 138 if (ctx->ticks) { 139 ticks = ctx->ticks; 140 if (ctx->expired && ctx->tintv.tv64) { 141 /* 142 * If tintv.tv64 != 0, this is a periodic timer that 143 * needs to be re-armed. We avoid doing it in the timer 144 * callback to avoid DoS attacks specifying a very 145 * short timer period. 146 */ 147 ticks += hrtimer_forward_now(&ctx->tmr, 148 ctx->tintv) - 1; 149 hrtimer_restart(&ctx->tmr); 150 } 151 ctx->expired = 0; 152 ctx->ticks = 0; 153 } 154 spin_unlock_irq(&ctx->wqh.lock); 155 if (ticks) 156 res = put_user(ticks, (u64 __user *) buf) ? -EFAULT: sizeof(ticks); 157 return res; 158 } 159 160 static const struct file_operations timerfd_fops = { 161 .release = timerfd_release, 162 .poll = timerfd_poll, 163 .read = timerfd_read, 164 }; 165 166 static struct file *timerfd_fget(int fd) 167 { 168 struct file *file; 169 170 file = fget(fd); 171 if (!file) 172 return ERR_PTR(-EBADF); 173 if (file->f_op != &timerfd_fops) { 174 fput(file); 175 return ERR_PTR(-EINVAL); 176 } 177 178 return file; 179 } 180 181 SYSCALL_DEFINE2(timerfd_create, int, clockid, int, flags) 182 { 183 int ufd; 184 struct timerfd_ctx *ctx; 185 186 /* Check the TFD_* constants for consistency. */ 187 BUILD_BUG_ON(TFD_CLOEXEC != O_CLOEXEC); 188 BUILD_BUG_ON(TFD_NONBLOCK != O_NONBLOCK); 189 190 if ((flags & ~TFD_CREATE_FLAGS) || 191 (clockid != CLOCK_MONOTONIC && 192 clockid != CLOCK_REALTIME)) 193 return -EINVAL; 194 195 ctx = kzalloc(sizeof(*ctx), GFP_KERNEL); 196 if (!ctx) 197 return -ENOMEM; 198 199 init_waitqueue_head(&ctx->wqh); 200 ctx->clockid = clockid; 201 hrtimer_init(&ctx->tmr, clockid, HRTIMER_MODE_ABS); 202 203 ufd = anon_inode_getfd("[timerfd]", &timerfd_fops, ctx, 204 O_RDWR | (flags & TFD_SHARED_FCNTL_FLAGS)); 205 if (ufd < 0) 206 kfree(ctx); 207 208 return ufd; 209 } 210 211 SYSCALL_DEFINE4(timerfd_settime, int, ufd, int, flags, 212 const struct itimerspec __user *, utmr, 213 struct itimerspec __user *, otmr) 214 { 215 struct file *file; 216 struct timerfd_ctx *ctx; 217 struct itimerspec ktmr, kotmr; 218 219 if (copy_from_user(&ktmr, utmr, sizeof(ktmr))) 220 return -EFAULT; 221 222 if ((flags & ~TFD_SETTIME_FLAGS) || 223 !timespec_valid(&ktmr.it_value) || 224 !timespec_valid(&ktmr.it_interval)) 225 return -EINVAL; 226 227 file = timerfd_fget(ufd); 228 if (IS_ERR(file)) 229 return PTR_ERR(file); 230 ctx = file->private_data; 231 232 /* 233 * We need to stop the existing timer before reprogramming 234 * it to the new values. 235 */ 236 for (;;) { 237 spin_lock_irq(&ctx->wqh.lock); 238 if (hrtimer_try_to_cancel(&ctx->tmr) >= 0) 239 break; 240 spin_unlock_irq(&ctx->wqh.lock); 241 cpu_relax(); 242 } 243 244 /* 245 * If the timer is expired and it's periodic, we need to advance it 246 * because the caller may want to know the previous expiration time. 247 * We do not update "ticks" and "expired" since the timer will be 248 * re-programmed again in the following timerfd_setup() call. 249 */ 250 if (ctx->expired && ctx->tintv.tv64) 251 hrtimer_forward_now(&ctx->tmr, ctx->tintv); 252 253 kotmr.it_value = ktime_to_timespec(timerfd_get_remaining(ctx)); 254 kotmr.it_interval = ktime_to_timespec(ctx->tintv); 255 256 /* 257 * Re-program the timer to the new value ... 258 */ 259 timerfd_setup(ctx, flags, &ktmr); 260 261 spin_unlock_irq(&ctx->wqh.lock); 262 fput(file); 263 if (otmr && copy_to_user(otmr, &kotmr, sizeof(kotmr))) 264 return -EFAULT; 265 266 return 0; 267 } 268 269 SYSCALL_DEFINE2(timerfd_gettime, int, ufd, struct itimerspec __user *, otmr) 270 { 271 struct file *file; 272 struct timerfd_ctx *ctx; 273 struct itimerspec kotmr; 274 275 file = timerfd_fget(ufd); 276 if (IS_ERR(file)) 277 return PTR_ERR(file); 278 ctx = file->private_data; 279 280 spin_lock_irq(&ctx->wqh.lock); 281 if (ctx->expired && ctx->tintv.tv64) { 282 ctx->expired = 0; 283 ctx->ticks += 284 hrtimer_forward_now(&ctx->tmr, ctx->tintv) - 1; 285 hrtimer_restart(&ctx->tmr); 286 } 287 kotmr.it_value = ktime_to_timespec(timerfd_get_remaining(ctx)); 288 kotmr.it_interval = ktime_to_timespec(ctx->tintv); 289 spin_unlock_irq(&ctx->wqh.lock); 290 fput(file); 291 292 return copy_to_user(otmr, &kotmr, sizeof(kotmr)) ? -EFAULT: 0; 293 } 294 295