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* [RFC] io_uring: fix the dead lock between io_uring and core dump
@ 2025-02-26 11:39 Haifeng Xu
  2025-02-27 13:09 ` kernel test robot
  2025-02-27 18:24 ` kernel test robot
  0 siblings, 2 replies; 4+ messages in thread
From: Haifeng Xu @ 2025-02-26 11:39 UTC (permalink / raw)
  To: asml.silence, axboe, ebiederm; +Cc: olivier, io-uring, linux-kernel, Haifeng Xu

In our production environment, we found many hung tasks.

	Thead A (exit_mm)
	...
		if (core_state) {
		struct core_thread self;

		mmap_read_unlock(mm);

		self.task = current;
		if (self.task->flags & PF_SIGNALED)
			self.next = xchg(&core_state->dumper.next, &self);
		else
			self.task = NULL;
		/*
		 * Implies mb(), the result of xchg() must be visible
		 * to core_state->dumper.
		 */
		if (atomic_dec_and_test(&core_state->nr_threads))
			complete(&core_state->startup);

		for (;;) {
			set_current_state(TASK_UNINTERRUPTIBLE);
			if (!self.task) /* see coredump_finish() */
				break;
			freezable_schedule();
		}
		__set_current_state(TASK_RUNNING);
		mmap_read_lock(mm);
	}
	...

	Thead B (coredump_wait)
	...
		if (core_waiters > 0) {
		struct core_thread *ptr;

		freezer_do_not_count();
		wait_for_completion(&core_state->startup);
		freezer_count();
		/*
		 * Wait for all the threads to become inactive, so that
		 * all the thread context (extended register state, like
		 * fpu etc) gets copied to the memory.
		 */
		ptr = core_state->dumper.next;
		while (ptr != NULL) {
			wait_task_inactive(ptr->task, 0);
			ptr = ptr->next;
		}
	...

	Thead C (io_worker_exit)
	...
		if (refcount_dec_and_test(&worker->ref))
		complete(&worker->ref_done);
		wait_for_completion(&worker->ref_done);
	...

Thread A is waiting Thead B to finish core dump, but Thead B found that there is
still one thread which doesn't step into exit_mm() to dec core_state->nr_threads.
The thead is Thread C, it has submitted a task_work (create_worker_cb) to Thread B
and then wait Thread B to execute or cancel the work. So this causes deadlock between
io_uring and core dump.

Our kernel vesion is stable 5.15.125, and the commit 1d5f5ea7cb7d ("io-wq: remove worker to owner tw dependency")
is included. When the last io woker exits, it doesn't find any callback. Once scheduled out,
it will invoke io_wq_worker_sleeping() to submit a task work to the master thread. So the
commit 1d5f5ea7cb7d ("io-wq: remove worker to owner tw dependency") won't help in this case.

For the core dump thread, we can set a timeout to check whether the taks_work callback exists,
If needed, cancel the task_work and wake up the io worker, so the dead lock will be resolved.

Signed-off-by: Haifeng Xu <haifeng.xu@shopee.com>
---
 fs/coredump.c              |  6 ++++--
 include/linux/completion.h |  2 ++
 io_uring/io-wq.c           |  3 +--
 io_uring/io-wq.h           |  1 +
 kernel/sched/completion.c  | 11 +++++++++++
 kernel/sched/core.c        |  6 ++++++
 6 files changed, 25 insertions(+), 4 deletions(-)

diff --git a/fs/coredump.c b/fs/coredump.c
index 591700e1b2ce..1d972d5882f0 100644
--- a/fs/coredump.c
+++ b/fs/coredump.c
@@ -42,6 +42,7 @@
 #include <linux/path.h>
 #include <linux/timekeeping.h>
 #include <linux/sysctl.h>
+#include <linux/sched/sysctl.h>
 #include <linux/elf.h>
 
 #include <linux/uaccess.h>
@@ -406,6 +407,7 @@ static int coredump_wait(int exit_code, struct core_state *core_state)
 {
 	struct task_struct *tsk = current;
 	int core_waiters = -EBUSY;
+	unsigned long hang_check = sysctl_hung_task_timeout_secs;
 
 	init_completion(&core_state->startup);
 	core_state->dumper.task = tsk;
@@ -415,8 +417,8 @@ static int coredump_wait(int exit_code, struct core_state *core_state)
 	if (core_waiters > 0) {
 		struct core_thread *ptr;
 
-		wait_for_completion_state(&core_state->startup,
-					  TASK_UNINTERRUPTIBLE|TASK_FREEZABLE);
+		wait_for_completion_state_timeout(&core_state->startup, TASK_UNINTERRUPTIBLE|TASK_FREEZABLE,
+						  hang_check * (HZ/2));
 		/*
 		 * Wait for all the threads to become inactive, so that
 		 * all the thread context (extended register state, like
diff --git a/include/linux/completion.h b/include/linux/completion.h
index fb2915676574..432de8ecc32d 100644
--- a/include/linux/completion.h
+++ b/include/linux/completion.h
@@ -104,6 +104,8 @@ extern void wait_for_completion_io(struct completion *);
 extern int wait_for_completion_interruptible(struct completion *x);
 extern int wait_for_completion_killable(struct completion *x);
 extern int wait_for_completion_state(struct completion *x, unsigned int state);
+extern int wait_for_completion_state_timeout(struct completion *x, unsigned int state,
+					     unsigned long timeout);
 extern unsigned long wait_for_completion_timeout(struct completion *x,
 						   unsigned long timeout);
 extern unsigned long wait_for_completion_io_timeout(struct completion *x,
diff --git a/io_uring/io-wq.c b/io_uring/io-wq.c
index 91019b4d0308..1c03dc57a3b3 100644
--- a/io_uring/io-wq.c
+++ b/io_uring/io-wq.c
@@ -141,7 +141,6 @@ static bool io_acct_cancel_pending_work(struct io_wq *wq,
 					struct io_wq_acct *acct,
 					struct io_cb_cancel_data *match);
 static void create_worker_cb(struct callback_head *cb);
-static void io_wq_cancel_tw_create(struct io_wq *wq);
 
 static bool io_worker_get(struct io_worker *worker)
 {
@@ -1230,7 +1229,7 @@ void io_wq_exit_start(struct io_wq *wq)
 	set_bit(IO_WQ_BIT_EXIT, &wq->state);
 }
 
-static void io_wq_cancel_tw_create(struct io_wq *wq)
+void io_wq_cancel_tw_create(struct io_wq *wq)
 {
 	struct callback_head *cb;
 
diff --git a/io_uring/io-wq.h b/io_uring/io-wq.h
index b3b004a7b625..48ba66b5d0bd 100644
--- a/io_uring/io-wq.h
+++ b/io_uring/io-wq.h
@@ -43,6 +43,7 @@ struct io_wq_data {
 	free_work_fn *free_work;
 };
 
+void io_wq_cancel_tw_create(struct io_wq *wq);
 struct io_wq *io_wq_create(unsigned bounded, struct io_wq_data *data);
 void io_wq_exit_start(struct io_wq *wq);
 void io_wq_put_and_exit(struct io_wq *wq);
diff --git a/kernel/sched/completion.c b/kernel/sched/completion.c
index 3561ab533dd4..9e7936a3cad4 100644
--- a/kernel/sched/completion.c
+++ b/kernel/sched/completion.c
@@ -269,6 +269,17 @@ int __sched wait_for_completion_state(struct completion *x, unsigned int state)
 }
 EXPORT_SYMBOL(wait_for_completion_state);
 
+int __sched wait_for_completion_state_timeout(struct completion *x, unsigned int state,
+					      unsigned long timeout)
+{
+	long t = wait_for_common(x, timeout, state);
+
+	if (t == -ERESTARTSYS)
+		return t;
+	return 0;
+}
+EXPORT_SYMBOL(wait_for_completion_state_timeout);
+
 /**
  * wait_for_completion_killable_timeout: - waits for completion of a task (w/(to,killable))
  * @x:  holds the state of this particular completion
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 9aecd914ac69..1cbe48559163 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -6790,6 +6790,7 @@ static inline void sched_submit_work(struct task_struct *tsk)
 {
 	static DEFINE_WAIT_OVERRIDE_MAP(sched_map, LD_WAIT_CONFIG);
 	unsigned int task_flags;
+	struct io_uring_task *io_uring = tsk->io_uring;
 
 	/*
 	 * Establish LD_WAIT_CONFIG context to ensure none of the code called
@@ -6806,6 +6807,11 @@ static inline void sched_submit_work(struct task_struct *tsk)
 		wq_worker_sleeping(tsk);
 	else if (task_flags & PF_IO_WORKER)
 		io_wq_worker_sleeping(tsk);
+	else if ((task_flags & PF_DUMPCORE) && io_uring) {
+		struct io_wq *wq = io_uring->io_wq;
+
+		io_wq_cancel_tw_create(wq);
+	}
 
 	/*
 	 * spinlock and rwlock must not flush block requests.  This will
-- 
2.43.0


^ permalink raw reply related	[flat|nested] 4+ messages in thread
end of thread, other threads:[~2025-02-28  9:40 UTC | newest]

Thread overview: 4+ messages (download: mbox.gz follow: Atom feed
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2025-02-26 11:39 [RFC] io_uring: fix the dead lock between io_uring and core dump Haifeng Xu
2025-02-27 13:09 ` kernel test robot
2025-02-27 18:24 ` kernel test robot
2025-02-28  9:40   ` Haifeng Xu

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