The patch titled
Subject: kthread: fix task state in kthread worker if being frozen
has been added to the -mm mm-nonmm-unstable branch. Its filename is
kthread-fix-task-state-in-kthread-worker-if-being-frozen.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/kthread-fix-task-state-in-kthread-worker-if-being-frozen.patch
This patch will later appear in the mm-nonmm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Chen Yu <yu.c.chen@xxxxxxxxx>
Subject: kthread: fix task state in kthread worker if being frozen
Date: Tue, 27 Aug 2024 19:23:08 +0800
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]
Link: https://lkml.kernel.org/r/20240827112308.181081-1-yu.c.chen@xxxxxxxxx
Fixes: b56c0d8937e6 ("kthread: implement kthread_worker")
Signed-off-by: Chen Yu <yu.c.chen@xxxxxxxxx>
Suggested-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Suggested-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Andreas Gruenbacher <agruenba@xxxxxxxxxx>
Cc: David Gow <davidgow@xxxxxxxxxx>
Cc: Mateusz Guzik <mjguzik@xxxxxxxxx>
Cc: Mickaël Salaün <mic@xxxxxxxxxxx>
Cc: Tejun Heo <tj@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
kernel/kthread.c | 10 +++++++++-
1 file changed, 9 insertions(+), 1 deletion(-)
--- a/kernel/kthread.c~kthread-fix-task-state-in-kthread-worker-if-being-frozen
+++ a/kernel/kthread.c
@@ -845,8 +845,16 @@ repeat:
* 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();
_
Patches currently in -mm which might be from yu.c.chen@xxxxxxxxx are
kthread-fix-task-state-in-kthread-worker-if-being-frozen.patch
