+ kthread-fix-task-state-in-kthread-worker-if-being-frozen.patch added to mm-nonmm-unstable branch

+ kthread-fix-task-state-in-kthread-worker-if-being-frozen.patch added to mm-nonmm-unstable branch

[Andrew Morton]

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The patch titled
     Subject: kthread: fix task state in kthread worker if being frozen
has been added to the -mm mm-nonmm-unstable branch.  Its filename is
     kthread-fix-task-state-in-kthread-worker-if-being-frozen.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/kthread-fix-task-state-in-kthread-worker-if-being-frozen.patch

This patch will later appear in the mm-nonmm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Chen Yu <yu.c.chen@intel.com>
Subject: kthread: fix task state in kthread worker if being frozen
Date: Tue, 27 Aug 2024 19:23:08 +0800

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>
---

 kernel/kthread.c |   10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

--- a/kernel/kthread.c~kthread-fix-task-state-in-kthread-worker-if-being-frozen
+++ a/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();
_

Patches currently in -mm which might be from yu.c.chen@intel.com are

kthread-fix-task-state-in-kthread-worker-if-being-frozen.patch