The quilt patch titled Subject: kthread: unpark only parked kthread has been removed from the -mm tree. Its filename was kthread-unpark-only-parked-kthread.patch

This patch was dropped because it was merged into the mm-hotfixes-stable branch of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

------------------------------------------------------ From: Frederic Weisbecker frederic@kernel.org Subject: kthread: unpark only parked kthread Date: Fri, 13 Sep 2024 23:46:34 +0200

Calling into kthread unparking unconditionally is mostly harmless when the kthread is already unparked. The wake up is then simply ignored because the target is not in TASK_PARKED state.

However if the kthread is per CPU, the wake up is preceded by a call to kthread_bind() which expects the task to be inactive and in TASK_PARKED state, which obviously isn't the case if it is unparked.

As a result, calling kthread_stop() on an unparked per-cpu kthread triggers such a warning:

WARNING: CPU: 0 PID: 11 at kernel/kthread.c:525 __kthread_bind_mask kernel/kthread.c:525 <TASK> kthread_stop+0x17a/0x630 kernel/kthread.c:707 destroy_workqueue+0x136/0xc40 kernel/workqueue.c:5810 wg_destruct+0x1e2/0x2e0 drivers/net/wireguard/device.c:257 netdev_run_todo+0xe1a/0x1000 net/core/dev.c:10693 default_device_exit_batch+0xa14/0xa90 net/core/dev.c:11769 ops_exit_list net/core/net_namespace.c:178 [inline] cleanup_net+0x89d/0xcc0 net/core/net_namespace.c:640 process_one_work kernel/workqueue.c:3231 [inline] process_scheduled_works+0xa2c/0x1830 kernel/workqueue.c:3312 worker_thread+0x86d/0xd70 kernel/workqueue.c:3393 kthread+0x2f0/0x390 kernel/kthread.c:389 ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:147 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244 </TASK>

Fix this with skipping unecessary unparking while stopping a kthread.

Link: https://lkml.kernel.org/r/20240913214634.12557-1-frederic@kernel.org Fixes: 5c25b5ff89f0 ("workqueue: Tag bound workers with KTHREAD_IS_PER_CPU") Signed-off-by: Frederic Weisbecker frederic@kernel.org Reported-by: syzbot+943d34fa3cf2191e3068@syzkaller.appspotmail.com Tested-by: syzbot+943d34fa3cf2191e3068@syzkaller.appspotmail.com Suggested-by: Thomas Gleixner tglx@linutronix.de Cc: Hillf Danton hdanton@sina.com Cc: Tejun Heo tj@kernel.org Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

kernel/kthread.c | 2 ++ 1 file changed, 2 insertions(+)

--- a/kernel/kthread.c~kthread-unpark-only-parked-kthread +++ a/kernel/kthread.c @@ -623,6 +623,8 @@ void kthread_unpark(struct task_struct * { struct kthread *kthread = to_kthread(k);

+ if (!test_bit(KTHREAD_SHOULD_PARK, &kthread->flags)) + return; /* * Newly created kthread was parked when the CPU was offline. * The binding was lost and we need to set it again. _

Patches currently in -mm which might be from frederic@kernel.org are