From 6b9ccbc033cf179956a37fef3ee415bdc3029d2f Mon Sep 17 00:00:00 2001 From: Chen Yu Date: Tue, 27 Aug 2024 19:23:08 +0800 Subject: [PATCH] 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(). Fixes: b56c0d8937e6 ("kthread: implement kthread_worker") Suggested-by: Peter Zijlstra Suggested-by: Andrew Morton Signed-off-by: Chen Yu Signed-off-by: Peter Zijlstra (Intel) Link: https://lore.kernel.org/lkml/Zs2ZoAcUsZMX2B%2FI@chenyu5-mobl2/ [1] --- 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 @@ 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();