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Fri, 14 Mar 2025 07:43:22 -0700 (PDT) From: Lance Yang To: akpm@linux-foundation.org Cc: will@kernel.org, peterz@infradead.org, mingo@redhat.com, longman@redhat.com, mhiramat@kernel.org, anna.schumaker@oracle.com, boqun.feng@gmail.com, joel.granados@kernel.org, kent.overstreet@linux.dev, leonylgao@tencent.com, linux-kernel@vger.kernel.org, rostedt@goodmis.org, senozhatsky@chromium.org, tfiga@chromium.org, amaindex@outlook.com, Lance Yang , Mingzhe Yang Subject: [PATCH RESEND v2 1/3] hung_task: replace blocker_mutex with encoded blocker Date: Fri, 14 Mar 2025 22:42:58 +0800 Message-ID: <20250314144300.32542-2-ioworker0@gmail.com> X-Mailer: git-send-email 2.45.2 In-Reply-To: <20250314144300.32542-1-ioworker0@gmail.com> References: <20250314144300.32542-1-ioworker0@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" This patch replaces 'struct mutex *blocker_mutex' with 'unsigned long blocker', as only one blocker is active at a time. The blocker filed can store both the lock addrees and the lock type, with LSB used to encode the type as Masami suggested, making it easier to extend the feature to cover other types of locks. Also, once the lock type is determined, we can directly extract the address and cast it to a lock pointer ;) Suggested-by: Masami Hiramatsu (Google) Signed-off-by: Mingzhe Yang Signed-off-by: Lance Yang --- include/linux/hung_task.h | 94 +++++++++++++++++++++++++++++++++++++++ include/linux/sched.h | 2 +- kernel/hung_task.c | 15 ++++--- kernel/locking/mutex.c | 8 +++- 4 files changed, 111 insertions(+), 8 deletions(-) create mode 100644 include/linux/hung_task.h diff --git a/include/linux/hung_task.h b/include/linux/hung_task.h new file mode 100644 index 000000000000..64ced33b0d1f --- /dev/null +++ b/include/linux/hung_task.h @@ -0,0 +1,94 @@ +/* SPDX-License-Identifier: GPL-2.0-only */ +/* + * Detect Hung Task: detecting tasks stuck in D state + * + * Copyright (C) 2025 Tongcheng Travel (www.ly.com) + * Author: Lance Yang + */ +#ifndef __LINUX_HUNG_TASK_H +#define __LINUX_HUNG_TASK_H + +#include +#include +#include + +/* + * @blocker: Combines lock address and blocking type. + * + * Since lock pointers are at least 4-byte aligned(32-bit) or 8-byte + * aligned(64-bit). This leaves the 2 least bits (LSBs) of the pointer + * always zero. So we can use these bits to encode the specific blocking + * type. + * + * Type encoding: + * 00 - Blocked on mutex (BLOCKER_TYPE_MUTEX) + * 01 - Blocked on semaphore (BLOCKER_TYPE_SEM) + * 10 - Blocked on rt-mutex (BLOCKER_TYPE_RTMUTEX) + * 11 - Blocked on rw-semaphore (BLOCKER_TYPE_RWSEM) + */ +#define BLOCKER_TYPE_MUTEX 0x00UL +#define BLOCKER_TYPE_SEM 0x01UL +#define BLOCKER_TYPE_RTMUTEX 0x02UL +#define BLOCKER_TYPE_RWSEM 0x03UL + +#define BLOCKER_TYPE_MASK 0x03UL + +#ifdef CONFIG_DETECT_HUNG_TASK_BLOCKER +static inline void hung_task_set_blocker(void *lock, unsigned long type) +{ + unsigned long lock_ptr =3D (unsigned long)lock; + + WARN_ON_ONCE(!lock_ptr); + WARN_ON_ONCE(lock_ptr & BLOCKER_TYPE_MASK); + WARN_ON_ONCE(READ_ONCE(current->blocker)); + + /* + * If the lock pointer matches the BLOCKER_TYPE_MASK, return + * without writing anything. + */ + if (lock_ptr & BLOCKER_TYPE_MASK) + return; + + WRITE_ONCE(current->blocker, lock_ptr | type); +} + +static inline void hung_task_clear_blocker(void) +{ + WARN_ON_ONCE(!READ_ONCE(current->blocker)); + + WRITE_ONCE(current->blocker, 0UL); +} + +static inline bool hung_task_blocker_is_type(unsigned long blocker, + unsigned long type) +{ + WARN_ON_ONCE(!blocker); + + return (blocker & BLOCKER_TYPE_MASK) =3D=3D type; +} + +static inline void *hung_task_blocker_to_lock(unsigned long blocker) +{ + WARN_ON_ONCE(!blocker); + + return (void *)(blocker & ~BLOCKER_TYPE_MASK); +} +#else +static inline void hung_task_set_blocker(void *lock, unsigned long type) +{ +} +static inline void hung_task_clear_blocker(void) +{ +} +static inline bool hung_task_blocker_is_type(unsigned long blocker, + unsigned long type) +{ + return false; +} +static inline void *hung_task_blocker_to_lock(unsigned long blocker) +{ + return NULL; +} +#endif + +#endif /* __LINUX_HUNG_TASK_H */ diff --git a/include/linux/sched.h b/include/linux/sched.h index 1419d94c8e87..f27060dac499 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -1218,7 +1218,7 @@ struct task_struct { #endif =20 #ifdef CONFIG_DETECT_HUNG_TASK_BLOCKER - struct mutex *blocker_mutex; + unsigned long blocker; #endif =20 #ifdef CONFIG_DEBUG_ATOMIC_SLEEP diff --git a/kernel/hung_task.c b/kernel/hung_task.c index dc898ec93463..46eb6717564d 100644 --- a/kernel/hung_task.c +++ b/kernel/hung_task.c @@ -25,6 +25,10 @@ =20 #include =20 +#ifdef CONFIG_DETECT_HUNG_TASK_BLOCKER +#include +#endif + /* * The number of tasks checked: */ @@ -98,16 +102,17 @@ static struct notifier_block panic_block =3D { static void debug_show_blocker(struct task_struct *task) { struct task_struct *g, *t; - unsigned long owner; - struct mutex *lock; + unsigned long owner, blocker; =20 RCU_LOCKDEP_WARN(!rcu_read_lock_held(), "No rcu lock held"); =20 - lock =3D READ_ONCE(task->blocker_mutex); - if (!lock) + blocker =3D READ_ONCE(task->blocker); + if (!blocker || !hung_task_blocker_is_type(blocker, BLOCKER_TYPE_MUTEX)) return; =20 - owner =3D mutex_get_owner(lock); + owner =3D mutex_get_owner( + (struct mutex *)hung_task_blocker_to_lock(blocker)); + if (unlikely(!owner)) { pr_err("INFO: task %s:%d is blocked on a mutex, but the owner is not fou= nd.\n", task->comm, task->pid); diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c index 6a543c204a14..642d6398e0dd 100644 --- a/kernel/locking/mutex.c +++ b/kernel/locking/mutex.c @@ -42,6 +42,10 @@ # define MUTEX_WARN_ON(cond) #endif =20 +#ifdef CONFIG_DETECT_HUNG_TASK_BLOCKER +#include +#endif + void __mutex_init(struct mutex *lock, const char *name, struct lock_class_key *= key) { @@ -189,7 +193,7 @@ __mutex_add_waiter(struct mutex *lock, struct mutex_wai= ter *waiter, struct list_head *list) { #ifdef CONFIG_DETECT_HUNG_TASK_BLOCKER - WRITE_ONCE(current->blocker_mutex, lock); + hung_task_set_blocker(lock, BLOCKER_TYPE_MUTEX); #endif debug_mutex_add_waiter(lock, waiter, current); =20 @@ -207,7 +211,7 @@ __mutex_remove_waiter(struct mutex *lock, struct mutex_= waiter *waiter) =20 debug_mutex_remove_waiter(lock, waiter, current); #ifdef CONFIG_DETECT_HUNG_TASK_BLOCKER - WRITE_ONCE(current->blocker_mutex, NULL); + hung_task_clear_blocker(); #endif } =20 --=20 2.45.2 From nobody Wed Dec 17 20:42:18 2025 Received: from mail-pl1-f174.google.com (mail-pl1-f174.google.com [209.85.214.174]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id A4BA3201036 for ; 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Fri, 14 Mar 2025 07:43:29 -0700 (PDT) Received: from localhost.localdomain ([124.156.216.125]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-225c6ba7280sm29228835ad.147.2025.03.14.07.43.23 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Fri, 14 Mar 2025 07:43:29 -0700 (PDT) From: Lance Yang To: akpm@linux-foundation.org Cc: will@kernel.org, peterz@infradead.org, mingo@redhat.com, longman@redhat.com, mhiramat@kernel.org, anna.schumaker@oracle.com, boqun.feng@gmail.com, joel.granados@kernel.org, kent.overstreet@linux.dev, leonylgao@tencent.com, linux-kernel@vger.kernel.org, rostedt@goodmis.org, senozhatsky@chromium.org, tfiga@chromium.org, amaindex@outlook.com, Lance Yang , Mingzhe Yang Subject: [PATCH RESEND v2 2/3] hung_task: show the blocker task if the task is hung on semaphore Date: Fri, 14 Mar 2025 22:42:59 +0800 Message-ID: <20250314144300.32542-3-ioworker0@gmail.com> X-Mailer: git-send-email 2.45.2 In-Reply-To: <20250314144300.32542-1-ioworker0@gmail.com> References: <20250314144300.32542-1-ioworker0@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Inspired by mutex blocker tracking[1], this patch makes a trade-off to balance the overhead and utility of the hung task detector. Unlike mutexes, semaphores lack explicit ownership tracking, making it challenging to identify the root cause of hangs. To address this, we introduce a last_holder field to the semaphore structure, which is updated when a task successfully calls down() and cleared during up(). The assumption is that if a task is blocked on a semaphore, the holders must not have released it. While this does not guarantee that the last holder is one of the current blockers, it likely provides a practical hint for diagnosing semaphore-related stalls. With this change, the hung task detector can now show blocker task's info like below: [Thu Mar 13 15:18:38 2025] INFO: task cat:1803 blocked for more than 122 se= conds. [Thu Mar 13 15:18:38 2025] Tainted: G OE 6.14.0-rc3+ #= 14 [Thu Mar 13 15:18:38 2025] "echo 0 > /proc/sys/kernel/hung_task_timeout_sec= s" disables this message. [Thu Mar 13 15:18:38 2025] task:cat state:D stack:0 pid:180= 3 tgid:1803 ppid:1057 task_flags:0x400000 flags:0x00000004 [Thu Mar 13 15:18:38 2025] Call trace: [Thu Mar 13 15:18:38 2025] __switch_to+0x1ec/0x380 (T) [Thu Mar 13 15:18:38 2025] __schedule+0xc30/0x44f8 [Thu Mar 13 15:18:38 2025] schedule+0xb8/0x3b0 [Thu Mar 13 15:18:38 2025] schedule_timeout+0x1d0/0x208 [Thu Mar 13 15:18:38 2025] __down_common+0x2d4/0x6f8 [Thu Mar 13 15:18:38 2025] __down+0x24/0x50 [Thu Mar 13 15:18:38 2025] down+0xd0/0x140 [Thu Mar 13 15:18:38 2025] read_dummy+0x3c/0xa0 [hung_task_sem] [Thu Mar 13 15:18:38 2025] full_proxy_read+0xfc/0x1d0 [Thu Mar 13 15:18:38 2025] vfs_read+0x1a0/0x858 [Thu Mar 13 15:18:38 2025] ksys_read+0x100/0x220 [Thu Mar 13 15:18:38 2025] __arm64_sys_read+0x78/0xc8 [Thu Mar 13 15:18:38 2025] invoke_syscall+0xd8/0x278 [Thu Mar 13 15:18:38 2025] el0_svc_common.constprop.0+0xb8/0x298 [Thu Mar 13 15:18:38 2025] do_el0_svc+0x4c/0x88 [Thu Mar 13 15:18:38 2025] el0_svc+0x44/0x108 [Thu Mar 13 15:18:38 2025] el0t_64_sync_handler+0x134/0x160 [Thu Mar 13 15:18:38 2025] el0t_64_sync+0x1b8/0x1c0 [Thu Mar 13 15:18:38 2025] INFO: task cat:1803 blocked on a semaphore likel= y last held by task cat:1802 [Thu Mar 13 15:18:38 2025] task:cat state:S stack:0 pid:180= 2 tgid:1802 ppid:1057 task_flags:0x400000 flags:0x00000004 [Thu Mar 13 15:18:38 2025] Call trace: [Thu Mar 13 15:18:38 2025] __switch_to+0x1ec/0x380 (T) [Thu Mar 13 15:18:38 2025] __schedule+0xc30/0x44f8 [Thu Mar 13 15:18:38 2025] schedule+0xb8/0x3b0 [Thu Mar 13 15:18:38 2025] schedule_timeout+0xf4/0x208 [Thu Mar 13 15:18:38 2025] msleep_interruptible+0x70/0x130 [Thu Mar 13 15:18:38 2025] read_dummy+0x48/0xa0 [hung_task_sem] [Thu Mar 13 15:18:38 2025] full_proxy_read+0xfc/0x1d0 [Thu Mar 13 15:18:38 2025] vfs_read+0x1a0/0x858 [Thu Mar 13 15:18:38 2025] ksys_read+0x100/0x220 [Thu Mar 13 15:18:38 2025] __arm64_sys_read+0x78/0xc8 [Thu Mar 13 15:18:38 2025] invoke_syscall+0xd8/0x278 [Thu Mar 13 15:18:38 2025] el0_svc_common.constprop.0+0xb8/0x298 [Thu Mar 13 15:18:38 2025] do_el0_svc+0x4c/0x88 [Thu Mar 13 15:18:38 2025] el0_svc+0x44/0x108 [Thu Mar 13 15:18:38 2025] el0t_64_sync_handler+0x134/0x160 [Thu Mar 13 15:18:38 2025] el0t_64_sync+0x1b8/0x1c0 [1] https://lore.kernel.org/all/174046694331.2194069.15472952050240807469.s= tgit@mhiramat.tok.corp.google.com Suggested-by: Masami Hiramatsu (Google) Signed-off-by: Mingzhe Yang Signed-off-by: Lance Yang --- include/linux/semaphore.h | 15 ++++++++++- kernel/hung_task.c | 45 ++++++++++++++++++++++++------- kernel/locking/semaphore.c | 55 +++++++++++++++++++++++++++++++++----- 3 files changed, 98 insertions(+), 17 deletions(-) diff --git a/include/linux/semaphore.h b/include/linux/semaphore.h index 04655faadc2d..89706157e622 100644 --- a/include/linux/semaphore.h +++ b/include/linux/semaphore.h @@ -16,13 +16,25 @@ struct semaphore { raw_spinlock_t lock; unsigned int count; struct list_head wait_list; + +#ifdef CONFIG_DETECT_HUNG_TASK_BLOCKER + unsigned long last_holder; +#endif }; =20 +#ifdef CONFIG_DETECT_HUNG_TASK_BLOCKER +#define __LAST_HOLDER_SEMAPHORE_INITIALIZER \ + , .last_holder =3D 0UL +#else +#define __LAST_HOLDER_SEMAPHORE_INITIALIZER +#endif + #define __SEMAPHORE_INITIALIZER(name, n) \ { \ .lock =3D __RAW_SPIN_LOCK_UNLOCKED((name).lock), \ .count =3D n, \ - .wait_list =3D LIST_HEAD_INIT((name).wait_list), \ + .wait_list =3D LIST_HEAD_INIT((name).wait_list) \ + __LAST_HOLDER_SEMAPHORE_INITIALIZER \ } =20 /* @@ -47,5 +59,6 @@ extern int __must_check down_killable(struct semaphore *s= em); extern int __must_check down_trylock(struct semaphore *sem); extern int __must_check down_timeout(struct semaphore *sem, long jiffies); extern void up(struct semaphore *sem); +extern unsigned long sem_last_holder(struct semaphore *sem); =20 #endif /* __LINUX_SEMAPHORE_H */ diff --git a/kernel/hung_task.c b/kernel/hung_task.c index 46eb6717564d..f8cb5a0e14f7 100644 --- a/kernel/hung_task.c +++ b/kernel/hung_task.c @@ -102,31 +102,56 @@ static struct notifier_block panic_block =3D { static void debug_show_blocker(struct task_struct *task) { struct task_struct *g, *t; - unsigned long owner, blocker; + unsigned long owner, blocker, blocker_lock_type; =20 RCU_LOCKDEP_WARN(!rcu_read_lock_held(), "No rcu lock held"); =20 blocker =3D READ_ONCE(task->blocker); - if (!blocker || !hung_task_blocker_is_type(blocker, BLOCKER_TYPE_MUTEX)) + if (!blocker) return; =20 - owner =3D mutex_get_owner( - (struct mutex *)hung_task_blocker_to_lock(blocker)); + if (hung_task_blocker_is_type(blocker, BLOCKER_TYPE_MUTEX)) { + owner =3D mutex_get_owner( + (struct mutex *)hung_task_blocker_to_lock(blocker)); + blocker_lock_type =3D BLOCKER_TYPE_MUTEX; + } else if (hung_task_blocker_is_type(blocker, BLOCKER_TYPE_SEM)) { + owner =3D sem_last_holder( + (struct semaphore *)hung_task_blocker_to_lock(blocker)); + blocker_lock_type =3D BLOCKER_TYPE_SEM; + } else + return; =20 if (unlikely(!owner)) { - pr_err("INFO: task %s:%d is blocked on a mutex, but the owner is not fou= nd.\n", - task->comm, task->pid); + switch (blocker_lock_type) { + case BLOCKER_TYPE_MUTEX: + pr_err("INFO: task %s:%d is blocked on a mutex, but the owner is not fo= und.\n", + task->comm, task->pid); + break; + case BLOCKER_TYPE_SEM: + pr_err("INFO: task %s:%d is blocked on a semaphore, but the last holder= is not found.\n", + task->comm, task->pid); + break; + } return; } =20 /* Ensure the owner information is correct. */ for_each_process_thread(g, t) { - if ((unsigned long)t =3D=3D owner) { + if ((unsigned long)t !=3D owner) + continue; + + switch (blocker_lock_type) { + case BLOCKER_TYPE_MUTEX: pr_err("INFO: task %s:%d is blocked on a mutex likely owned by task %s:= %d.\n", - task->comm, task->pid, t->comm, t->pid); - sched_show_task(t); - return; + task->comm, task->pid, t->comm, t->pid); + break; + case BLOCKER_TYPE_SEM: + pr_err("INFO: task %s:%d blocked on a semaphore likely last held by tas= k %s:%d\n", + task->comm, task->pid, t->comm, t->pid); + break; } + sched_show_task(t); + return; } } #else diff --git a/kernel/locking/semaphore.c b/kernel/locking/semaphore.c index 34bfae72f295..87dfb93a812d 100644 --- a/kernel/locking/semaphore.c +++ b/kernel/locking/semaphore.c @@ -34,11 +34,16 @@ #include #include =20 +#ifdef CONFIG_DETECT_HUNG_TASK_BLOCKER +#include +#endif + static noinline void __down(struct semaphore *sem); static noinline int __down_interruptible(struct semaphore *sem); static noinline int __down_killable(struct semaphore *sem); static noinline int __down_timeout(struct semaphore *sem, long timeout); static noinline void __up(struct semaphore *sem); +static inline void __sem_acquire(struct semaphore *sem); =20 /** * down - acquire the semaphore @@ -58,7 +63,7 @@ void __sched down(struct semaphore *sem) might_sleep(); raw_spin_lock_irqsave(&sem->lock, flags); if (likely(sem->count > 0)) - sem->count--; + __sem_acquire(sem); else __down(sem); raw_spin_unlock_irqrestore(&sem->lock, flags); @@ -82,7 +87,7 @@ int __sched down_interruptible(struct semaphore *sem) might_sleep(); raw_spin_lock_irqsave(&sem->lock, flags); if (likely(sem->count > 0)) - sem->count--; + __sem_acquire(sem); else result =3D __down_interruptible(sem); raw_spin_unlock_irqrestore(&sem->lock, flags); @@ -109,7 +114,7 @@ int __sched down_killable(struct semaphore *sem) might_sleep(); raw_spin_lock_irqsave(&sem->lock, flags); if (likely(sem->count > 0)) - sem->count--; + __sem_acquire(sem); else result =3D __down_killable(sem); raw_spin_unlock_irqrestore(&sem->lock, flags); @@ -139,7 +144,7 @@ int __sched down_trylock(struct semaphore *sem) raw_spin_lock_irqsave(&sem->lock, flags); count =3D sem->count - 1; if (likely(count >=3D 0)) - sem->count =3D count; + __sem_acquire(sem); raw_spin_unlock_irqrestore(&sem->lock, flags); =20 return (count < 0); @@ -164,7 +169,7 @@ int __sched down_timeout(struct semaphore *sem, long ti= meout) might_sleep(); raw_spin_lock_irqsave(&sem->lock, flags); if (likely(sem->count > 0)) - sem->count--; + __sem_acquire(sem); else result =3D __down_timeout(sem, timeout); raw_spin_unlock_irqrestore(&sem->lock, flags); @@ -185,6 +190,12 @@ void __sched up(struct semaphore *sem) unsigned long flags; =20 raw_spin_lock_irqsave(&sem->lock, flags); + +#ifdef CONFIG_DETECT_HUNG_TASK_BLOCKER + if (READ_ONCE(sem->last_holder) =3D=3D (unsigned long)current) + WRITE_ONCE(sem->last_holder, 0UL); +#endif + if (likely(list_empty(&sem->wait_list))) sem->count++; else @@ -224,8 +235,12 @@ static inline int __sched ___down_common(struct semaph= ore *sem, long state, raw_spin_unlock_irq(&sem->lock); timeout =3D schedule_timeout(timeout); raw_spin_lock_irq(&sem->lock); - if (waiter.up) + if (waiter.up) { +#ifdef CONFIG_DETECT_HUNG_TASK_BLOCKER + WRITE_ONCE(sem->last_holder, (unsigned long)current); +#endif return 0; + } } =20 timed_out: @@ -242,10 +257,18 @@ static inline int __sched __down_common(struct semaph= ore *sem, long state, { int ret; =20 +#ifdef CONFIG_DETECT_HUNG_TASK_BLOCKER + hung_task_set_blocker(sem, BLOCKER_TYPE_SEM); +#endif + trace_contention_begin(sem, 0); ret =3D ___down_common(sem, state, timeout); trace_contention_end(sem, ret); =20 +#ifdef CONFIG_DETECT_HUNG_TASK_BLOCKER + hung_task_clear_blocker(); +#endif + return ret; } =20 @@ -277,3 +300,23 @@ static noinline void __sched __up(struct semaphore *se= m) waiter->up =3D true; wake_up_process(waiter->task); } + +#ifdef CONFIG_DETECT_HUNG_TASK_BLOCKER +unsigned long sem_last_holder(struct semaphore *sem) +{ + return READ_ONCE(sem->last_holder); 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Fri, 14 Mar 2025 07:43:36 -0700 (PDT) Received: from localhost.localdomain ([124.156.216.125]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-225c6ba7280sm29228835ad.147.2025.03.14.07.43.30 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Fri, 14 Mar 2025 07:43:35 -0700 (PDT) From: Lance Yang To: akpm@linux-foundation.org Cc: will@kernel.org, peterz@infradead.org, mingo@redhat.com, longman@redhat.com, mhiramat@kernel.org, anna.schumaker@oracle.com, boqun.feng@gmail.com, joel.granados@kernel.org, kent.overstreet@linux.dev, leonylgao@tencent.com, linux-kernel@vger.kernel.org, rostedt@goodmis.org, senozhatsky@chromium.org, tfiga@chromium.org, amaindex@outlook.com, Lance Yang Subject: [PATCH RESEND v2 3/3] samples: add hung_task detector semaphore blocking sample Date: Fri, 14 Mar 2025 22:43:00 +0800 Message-ID: <20250314144300.32542-4-ioworker0@gmail.com> X-Mailer: git-send-email 2.45.2 In-Reply-To: <20250314144300.32542-1-ioworker0@gmail.com> References: <20250314144300.32542-1-ioworker0@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Zi Li Add a hung_task detector semaphore blocking test sample code. This module will create a dummy file on the debugfs. That file will cause the read process to sleep for a sufficiently long time (256 seconds) while holding a semaphore. As a result, the second process will wait on the semaphore for a prolonged duration and be detected by the hung_task detector. Usage is; > cd /sys/kernel/debug/hung_task > cat semaphore & cat semaphore and wait for hung_task message. Signed-off-by: Lance Yang Signed-off-by: Zi Li --- samples/Kconfig | 11 ++-- samples/hung_task/Makefile | 3 +- samples/hung_task/hung_task_mutex.c | 20 ++++--- samples/hung_task/hung_task_semaphore.c | 74 +++++++++++++++++++++++++ 4 files changed, 96 insertions(+), 12 deletions(-) create mode 100644 samples/hung_task/hung_task_semaphore.c diff --git a/samples/Kconfig b/samples/Kconfig index 09011be2391a..3a073d6b848b 100644 --- a/samples/Kconfig +++ b/samples/Kconfig @@ -304,10 +304,13 @@ config SAMPLE_HUNG_TASK tristate "Hung task detector test code" depends on DETECT_HUNG_TASK && DEBUG_FS help - Build a module which provide a simple debugfs file. If user reads - the file, it will sleep long time (256 seconds) with holding a - mutex. Thus if there are 2 or more processes read this file, it - will be detected by the hung_task watchdog. + Build multiple modules to test the hung task detector. Each module + provides a simple debugfs file corresponding to a specific + synchronization primitive (e.g., mutex, semaphore, etc.). When the + file is read, the module will sleep for a long time (256 seconds) + while holding the respective synchronizer. If multiple processes + attempt to read these files concurrently, the hung_task watchdog + can detect potential hangs or deadlocks. =20 source "samples/rust/Kconfig" =20 diff --git a/samples/hung_task/Makefile b/samples/hung_task/Makefile index fe9dde799880..7483c2c0a0ef 100644 --- a/samples/hung_task/Makefile +++ b/samples/hung_task/Makefile @@ -1,2 +1,3 @@ # SPDX-License-Identifier: GPL-2.0-only -obj-$(CONFIG_SAMPLE_HUNG_TASK) +=3D hung_task_mutex.o \ No newline at end of file +obj-$(CONFIG_SAMPLE_HUNG_TASK) +=3D hung_task_mutex.o +obj-$(CONFIG_SAMPLE_HUNG_TASK) +=3D hung_task_semaphore.o \ No newline at end of file diff --git a/samples/hung_task/hung_task_mutex.c b/samples/hung_task/hung_t= ask_mutex.c index 7a29f2246d22..e4d1d69618b8 100644 --- a/samples/hung_task/hung_task_mutex.c +++ b/samples/hung_task/hung_task_mutex.c @@ -22,7 +22,7 @@ =20 static const char dummy_string[] =3D "This is a dummy string."; static DEFINE_MUTEX(dummy_mutex); -struct dentry *hung_task_dir; +static struct dentry *hung_task_dir; =20 static ssize_t read_dummy(struct file *file, char __user *user_buf, size_t count, loff_t *ppos) @@ -43,19 +43,25 @@ static const struct file_operations hung_task_fops =3D { =20 static int __init hung_task_sample_init(void) { - hung_task_dir =3D debugfs_create_dir(HUNG_TASK_DIR, NULL); - if (IS_ERR(hung_task_dir)) - return PTR_ERR(hung_task_dir); + hung_task_dir =3D debugfs_lookup(HUNG_TASK_DIR, NULL); + if (!hung_task_dir) { + hung_task_dir =3D debugfs_create_dir(HUNG_TASK_DIR, NULL); + if (IS_ERR(hung_task_dir)) + return PTR_ERR(hung_task_dir); + } =20 - debugfs_create_file(HUNG_TASK_FILE, 0400, hung_task_dir, - NULL, &hung_task_fops); + debugfs_create_file(HUNG_TASK_FILE, 0400, hung_task_dir, NULL, + &hung_task_fops); =20 return 0; } =20 static void __exit hung_task_sample_exit(void) { - debugfs_remove_recursive(hung_task_dir); + debugfs_lookup_and_remove(HUNG_TASK_FILE, hung_task_dir); + + if (simple_empty(hung_task_dir)) + debugfs_remove(hung_task_dir); } =20 module_init(hung_task_sample_init); diff --git a/samples/hung_task/hung_task_semaphore.c b/samples/hung_task/hu= ng_task_semaphore.c new file mode 100644 index 000000000000..a5814971bfb8 --- /dev/null +++ b/samples/hung_task/hung_task_semaphore.c @@ -0,0 +1,74 @@ +// SPDX-License-Identifier: GPL-2.0-or-later +/* + * hung_task_semaphore.c - Sample code which causes hung task by semaphore + * + * Usage: load this module and read `/hung_task/semaphore` + * by 2 or more processes. + * + * This is for testing kernel hung_task error message. + * Note that this will make your system freeze and maybe + * cause panic. So do not use this except for the test. + */ + +#include +#include +#include +#include +#include + +#define HUNG_TASK_DIR "hung_task" +#define HUNG_TASK_FILE "semaphore" +#define SLEEP_SECOND 256 + +static const char dummy_string[] =3D "This is a dummy string."; +static DEFINE_SEMAPHORE(dummy_sem, 1); +static struct dentry *hung_task_dir; + +static ssize_t read_dummy(struct file *file, char __user *user_buf, + size_t count, loff_t *ppos) +{ + /* If the second task waits on the semaphore, it is uninterruptible sleep= . */ + down(&dummy_sem); + + /* When the first task sleep here, it is interruptible. */ + msleep_interruptible(SLEEP_SECOND * 1000); + + up(&dummy_sem); + + return simple_read_from_buffer(user_buf, count, ppos, dummy_string, + sizeof(dummy_string)); +} + +static const struct file_operations hung_task_fops =3D { + .read =3D read_dummy, +}; + +static int __init hung_task_sample_init(void) +{ + hung_task_dir =3D debugfs_lookup(HUNG_TASK_DIR, NULL); + if (!hung_task_dir) { + hung_task_dir =3D debugfs_create_dir(HUNG_TASK_DIR, NULL); + if (IS_ERR(hung_task_dir)) + return PTR_ERR(hung_task_dir); + } + + debugfs_create_file(HUNG_TASK_FILE, 0400, hung_task_dir, NULL, + &hung_task_fops); + + return 0; +} + +static void __exit hung_task_sample_exit(void) +{ + debugfs_lookup_and_remove(HUNG_TASK_FILE, hung_task_dir); + + if (simple_empty(hung_task_dir)) + debugfs_remove(hung_task_dir); +} + +module_init(hung_task_sample_init); +module_exit(hung_task_sample_exit); + +MODULE_LICENSE("GPL"); +MODULE_AUTHOR("Zi Li"); +MODULE_DESCRIPTION("Simple sleep under semaphore file for testing hung tas= k"); --=20 2.45.2