[PATCH 6.11 303/695] kthread: fix task state in kthread worker if being frozen

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6.11-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Chen Yu <yu.c.chen@xxxxxxxxx>

[ 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@xxxxxxxxx
Fixes: b56c0d8937e6 ("kthread: implement kthread_worker")
Signed-off-by: Chen Yu <yu.c.chen@xxxxxxxxx>
Suggested-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Suggested-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Andreas Gruenbacher <agruenba@xxxxxxxxxx>
Cc: David Gow <davidgow@xxxxxxxxxx>
Cc: Mateusz Guzik <mjguzik@xxxxxxxxx>
Cc: Mickaël Salaün <mic@xxxxxxxxxxx>
Cc: Tejun Heo <tj@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 kernel/kthread.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/kernel/kthread.c b/kernel/kthread.c
index f7be976ff88af..db4ceb0f503cc 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -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();
-- 
2.43.0







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