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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 * Type encoding:
24 * 00 - Blocked on mutex (BLOCKER_TYPE_MUTEX)
25 * 01 - Blocked on semaphore (BLOCKER_TYPE_SEM)
26 * 10 - Blocked on rt-mutex (BLOCKER_TYPE_RTMUTEX)
27 * 11 - Blocked on rw-semaphore (BLOCKER_TYPE_RWSEM)
28 */
29#define BLOCKER_TYPE_MUTEX 0x00UL
30#define BLOCKER_TYPE_SEM 0x01UL
31#define BLOCKER_TYPE_RTMUTEX 0x02UL
32#define BLOCKER_TYPE_RWSEM 0x03UL
33
34#define BLOCKER_TYPE_MASK 0x03UL
35
36#ifdef CONFIG_DETECT_HUNG_TASK_BLOCKER
37static inline void hung_task_set_blocker(void *lock, unsigned long type)
38{
39 unsigned long lock_ptr = (unsigned long)lock;
40
41 WARN_ON_ONCE(!lock_ptr);
42 WARN_ON_ONCE(READ_ONCE(current->blocker));
43
44 /*
45 * If the lock pointer matches the BLOCKER_TYPE_MASK, return
46 * without writing anything.
47 */
48 if (WARN_ON_ONCE(lock_ptr & BLOCKER_TYPE_MASK))
49 return;
50
51 WRITE_ONCE(current->blocker, lock_ptr | type);
52}
53
54static inline void hung_task_clear_blocker(void)
55{
56 WARN_ON_ONCE(!READ_ONCE(current->blocker));
57
58 WRITE_ONCE(current->blocker, 0UL);
59}
60
61/*
62 * hung_task_get_blocker_type - Extracts blocker type from encoded blocker
63 * address.
64 *
65 * @blocker: Blocker pointer with encoded type (via LSB bits)
66 *
67 * Returns: BLOCKER_TYPE_MUTEX, BLOCKER_TYPE_SEM, etc.
68 */
69static inline unsigned long hung_task_get_blocker_type(unsigned long blocker)
70{
71 WARN_ON_ONCE(!blocker);
72
73 return blocker & BLOCKER_TYPE_MASK;
74}
75
76static inline void *hung_task_blocker_to_lock(unsigned long blocker)
77{
78 WARN_ON_ONCE(!blocker);
79
80 return (void *)(blocker & ~BLOCKER_TYPE_MASK);
81}
82#else
83static inline void hung_task_set_blocker(void *lock, unsigned long type)
84{
85}
86static inline void hung_task_clear_blocker(void)
87{
88}
89static inline unsigned long hung_task_get_blocker_type(unsigned long blocker)
90{
91 return 0UL;
92}
93static inline void *hung_task_blocker_to_lock(unsigned long blocker)
94{
95 return NULL;
96}
97#endif
98
99#endif /* __LINUX_HUNG_TASK_H */