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Message-Id: <20240827112308.181081-1-yu.c.chen@intel.com>
Date: Tue, 27 Aug 2024 19:23:08 +0800
From: Chen Yu <yu.c.chen@...el.com>
To: Andrew Morton <akpm@...ux-foundation.org>,
Peter Zijlstra <peterz@...radead.org>
Cc: Mateusz Guzik <mjguzik@...il.com>,
Mickael Salaun <mic@...ikod.net>,
Tejun Heo <tj@...nel.org>,
David Gow <davidgow@...gle.com>,
Andreas Gruenbacher <agruenba@...hat.com>,
linux-kernel@...r.kernel.org,
Chen Yu <yu.c.chen@...el.com>
Subject: [PATCH v2] kthread: fix task state in kthread worker if being frozen
When analyzing a kernel waring message, Peter pointed out that there is a race
condition when the kworker is being frozen and falls into try_to_freeze() with
TASK_INTERRUPTIBLE, which could trigger a might_sleep() warning in try_to_freeze().
Although the root cause is not related to freeze()[1], it is still worthy to fix
this issue ahead.
One possible race scenario:
CPU 0 CPU 1
----- -----
// kthread_worker_fn
set_current_state(TASK_INTERRUPTIBLE);
suspend_freeze_processes()
freeze_processes
static_branch_inc(&freezer_active);
freeze_kernel_threads
pm_nosig_freezing = true;
if (work) { //false
__set_current_state(TASK_RUNNING);
} else if (!freezing(current)) //false, been frozen
freezing():
if (static_branch_unlikely(&freezer_active))
if (pm_nosig_freezing)
return true;
schedule()
}
// state is still TASK_INTERRUPTIBLE
try_to_freeze()
might_sleep() <--- warning
Fix this by explicitly set the TASK_RUNNING before entering
try_to_freeze().
Link: https://lore.kernel.org/lkml/Zs2ZoAcUsZMX2B%2FI@chenyu5-mobl2/ [1]
Fixes: b56c0d8937e6 ("kthread: implement kthread_worker")
Suggested-by: Peter Zijlstra <peterz@...radead.org>
Suggested-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Chen Yu <yu.c.chen@...el.com>
---
v1->v2: Describe the race condition in commit log and
refined the code. (Andrew Morton)
---
kernel/kthread.c | 10 +++++++++-
1 file changed, 9 insertions(+), 1 deletion(-)
diff --git a/kernel/kthread.c b/kernel/kthread.c
index f7be976ff88a..db4ceb0f503c 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -845,8 +845,16 @@ int kthread_worker_fn(void *worker_ptr)
* event only cares about the address.
*/
trace_sched_kthread_work_execute_end(work, func);
- } else if (!freezing(current))
+ } else if (!freezing(current)) {
schedule();
+ } else {
+ /*
+ * Handle the case where the current remains
+ * TASK_INTERRUPTIBLE. try_to_freeze() expects
+ * the current to be TASK_RUNNING.
+ */
+ __set_current_state(TASK_RUNNING);
+ }
try_to_freeze();
cond_resched();
--
2.25.1
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