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@xxxxxxxxxx>
---
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
