6.6-stable review patch. If anyone has any objections, please let me know.
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From: Chen Yu yu.c.chen@intel.com
[ 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 290cbc845225e..ac03bc55e17ca 100644 --- a/kernel/kthread.c +++ b/kernel/kthread.c @@ -844,8 +844,16 @@ 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();