hung_task.h

  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 */