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kthread: fix task state in kthread worker if being frozen

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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: b56c0d8937 ("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>
This commit is contained in:
Chen Yu 2024-08-27 19:23:08 +08:00 committed by Andrew Morton
parent 7e10835989
commit e16c7b0778
1 changed files with 9 additions and 1 deletions
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10
kernel/kthread.c
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@ -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();