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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 * 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
41static 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
58static 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 */
71static 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
78static 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
85static inline void hung_task_set_blocker(void *lock, unsigned long type)
86{
87}
88static inline void hung_task_clear_blocker(void)
89{
90}
91static inline unsigned long hung_task_get_blocker_type(unsigned long blocker)
92{
93 return 0UL;
94}
95static inline void *hung_task_blocker_to_lock(unsigned long blocker)
96{
97 return NULL;
98}
99#endif
100
101#endif /* __LINUX_HUNG_TASK_H */