1 /* SPDX-License-Identifier: GPL-2.0-only */
2 /*
3 * Detect Hung Task: detecting tasks stuck in D state
4 *
5 * Copyright (C) 2025 Tongcheng Travel (www.ly.com)
6 * Author: Lance Yang <mingzhe.yang@ly.com>
7 */
8 #ifndef __LINUX_HUNG_TASK_H
9 #define __LINUX_HUNG_TASK_H
10
11 #include <linux/bug.h>
12 #include <linux/sched.h>
13 #include <linux/compiler.h>
14
15 /*
16 * @blocker: Combines lock address and blocking type.
17 *
18 * Since lock pointers are at least 4-byte aligned(32-bit) or 8-byte
19 * aligned(64-bit). This leaves the 2 least bits (LSBs) of the pointer
20 * always zero. So we can use these bits to encode the specific blocking
21 * type.
22 *
23 * Note that on architectures where this is not guaranteed, or for any
24 * unaligned lock, this tracking mechanism is silently skipped for that
25 * lock.
26 *
27 * Type encoding:
28 * 00 - Blocked on mutex (BLOCKER_TYPE_MUTEX)
29 * 01 - Blocked on semaphore (BLOCKER_TYPE_SEM)
30 * 10 - Blocked on rw-semaphore as READER (BLOCKER_TYPE_RWSEM_READER)
31 * 11 - Blocked on rw-semaphore as WRITER (BLOCKER_TYPE_RWSEM_WRITER)
32 */
33 #define BLOCKER_TYPE_MUTEX 0x00UL
34 #define BLOCKER_TYPE_SEM 0x01UL
35 #define BLOCKER_TYPE_RWSEM_READER 0x02UL
36 #define BLOCKER_TYPE_RWSEM_WRITER 0x03UL
37
38 #define BLOCKER_TYPE_MASK 0x03UL
39
40 #ifdef CONFIG_DETECT_HUNG_TASK_BLOCKER
hung_task_set_blocker(void * lock,unsigned long type)41 static inline void hung_task_set_blocker(void *lock, unsigned long type)
42 {
43 unsigned long lock_ptr = (unsigned long)lock;
44
45 WARN_ON_ONCE(!lock_ptr);
46 WARN_ON_ONCE(READ_ONCE(current->blocker));
47
48 /*
49 * If the lock pointer matches the BLOCKER_TYPE_MASK, return
50 * without writing anything.
51 */
52 if (lock_ptr & BLOCKER_TYPE_MASK)
53 return;
54
55 WRITE_ONCE(current->blocker, lock_ptr | type);
56 }
57
hung_task_clear_blocker(void)58 static inline void hung_task_clear_blocker(void)
59 {
60 WRITE_ONCE(current->blocker, 0UL);
61 }
62
63 /*
64 * hung_task_get_blocker_type - Extracts blocker type from encoded blocker
65 * address.
66 *
67 * @blocker: Blocker pointer with encoded type (via LSB bits)
68 *
69 * Returns: BLOCKER_TYPE_MUTEX, BLOCKER_TYPE_SEM, etc.
70 */
hung_task_get_blocker_type(unsigned long blocker)71 static inline unsigned long hung_task_get_blocker_type(unsigned long blocker)
72 {
73 WARN_ON_ONCE(!blocker);
74
75 return blocker & BLOCKER_TYPE_MASK;
76 }
77
hung_task_blocker_to_lock(unsigned long blocker)78 static inline void *hung_task_blocker_to_lock(unsigned long blocker)
79 {
80 WARN_ON_ONCE(!blocker);
81
82 return (void *)(blocker & ~BLOCKER_TYPE_MASK);
83 }
84 #else
hung_task_set_blocker(void * lock,unsigned long type)85 static inline void hung_task_set_blocker(void *lock, unsigned long type)
86 {
87 }
hung_task_clear_blocker(void)88 static inline void hung_task_clear_blocker(void)
89 {
90 }
hung_task_get_blocker_type(unsigned long blocker)91 static inline unsigned long hung_task_get_blocker_type(unsigned long blocker)
92 {
93 return 0UL;
94 }
hung_task_blocker_to_lock(unsigned long blocker)95 static inline void *hung_task_blocker_to_lock(unsigned long blocker)
96 {
97 return NULL;
98 }
99 #endif
100
101 #endif /* __LINUX_HUNG_TASK_H */
102