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().

Link: https://lore.kernel.org/lkml/Zs2ZoAcUsZMX2B%2FI@chenyu5-mobl2/ [1]
Link: https://lkml.kernel.org/r/[email protected]
Fixes: b56c0d8937e6 ("kthread: implement kthread_worker")
Signed-off-by: Chen Yu <[email protected]>
Suggested-by: Peter Zijlstra <[email protected]>
Suggested-by: Andrew Morton <[email protected]>
Cc: Andreas Gruenbacher <[email protected]>
Cc: David Gow <[email protected]>
Cc: Mateusz Guzik <[email protected]>
Cc: Mickaël Salaün <[email protected]>
Cc: Tejun Heo <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

0 files changed, 0 insertions, 0 deletions