From b1ce87a881ee31afdc110ce702b8a17b7f3b0d44 Mon Sep 17 00:00:00 2001 From: Chen Yu <yu.c.chen@intel.com> Date: Tue, 27 Aug 2024 19:23:08 +0800 Subject: [PATCH] kthread: fix task state in kthread worker if being frozen MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit [ Upstream commit e16c7b07784f3fb03025939c4590b9a7c64970a7 ] 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@intel.com Fixes: b56c0d8937e6 ("kthread: implement kthread_worker") Signed-off-by: Chen Yu <yu.c.chen@intel.com> Suggested-by: Peter Zijlstra <peterz@infradead.org> Suggested-by: Andrew Morton <akpm@linux-foundation.org> Cc: Andreas Gruenbacher <agruenba@redhat.com> Cc: David Gow <davidgow@google.com> Cc: Mateusz Guzik <mjguzik@gmail.com> Cc: Mickaël Salaün <mic@digikod.net> Cc: Tejun Heo <tj@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Sasha Levin <sashal@kernel.org> --- kernel/kthread.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) diff --git a/kernel/kthread.c b/kernel/kthread.c index ba8502ee9..3da2fbb86 100755 --- a/kernel/kthread.c +++ b/kernel/kthread.c @@ -783,8 +783,16 @@ 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();