FAILED: patch "[PATCH] media: s5p-mfc: use timer_shutdown_sync() for the" failed to apply to 6.6-stable tree

The patch below does not apply to the 6.6-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.6.y
git checkout FETCH_HEAD
git cherry-pick -x 63069b5917cba2e15b1a78b3f4ff99e45102c56f
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026110426-scrutiny-value-3242@gregkh' --subject-prefix 'PATCH 6.6.y' 'HEAD^..'

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 63069b5917cba2e15b1a78b3f4ff99e45102c56f Mon Sep 17 00:00:00 2001
From: Fan Wu <[email protected]>
Date: Thu, 30 Jul 2026 07:15:52 +0000
Subject: [PATCH] media: s5p-mfc: use timer_shutdown_sync() for the
self-rearming watchdog

The MFC watchdog timer (s5p_mfc_watchdog) is self-rearming: every callback re-arms itself with add_timer() and, on a timeout, schedules watchdog_work. s5p_mfc_remove() tears this down with timer_delete_sync() followed by flush_work().

timer_delete_sync() dequeues the timer and waits for a callback that is already running, but it does not prevent a subsequent re-arm. Because the watchdog callback re-arms via add_timer(), this is the wrong shutdown
primitive: once the wait returns nothing guarantees a just-queued re-arm will not fire later, dereferencing dev (clock on/off, deinit_hw, load_firmware, init_hw) after video_unregister_device(), DMA teardown and s5p_mfc_final_pm() have run, a potential use-after-free.

Use timer_shutdown_sync(), which puts the timer into a shutdown state so that any add_timer()/mod_timer() from the callback becomes a no-op and no later firing is possible. Switch flush_work() to cancel_work_sync() so any watchdog_work that was already queued before the timer was stopped is cancelled rather than allowed to run to completion against the torn-down device.

This issue was found by an in-house static analysis tool. No runtime reproducer is available.

index 32eb402d439c..03e7eac8d1f7 100644
@@ -1474,8 +1474,8 @@ static void s5p_mfc_remove(struct platform_device *pdev)
 	}
 	mutex_unlock(&dev->mfc_mutex);
 
-	timer_delete_sync(&dev->watchdog_timer);
-	flush_work(&dev->watchdog_work);
+	timer_shutdown_sync(&dev->watchdog_timer);
+	cancel_work_sync(&dev->watchdog_work);
 
 	video_unregister_device(dev->vfd_enc);
 	video_unregister_device(dev->vfd_dec);

From: Fan Wu <[email protected]>

[ Upstream commit 63069b5917cba2e15b1a78b3f4ff99e45102c56f ]

The MFC watchdog timer (s5p_mfc_watchdog) is self-rearming: every callback re-arms itself with add_timer() and, on a timeout, schedules watchdog_work. s5p_mfc_remove() tears this down with timer_delete_sync() followed by flush_work().

timer_delete_sync() dequeues the timer and waits for a callback that is already running, but it does not prevent a subsequent re-arm. Because the watchdog callback re-arms via add_timer(), this is the wrong shutdown
primitive: once the wait returns nothing guarantees a just-queued re-arm will not fire later, dereferencing dev (clock on/off, deinit_hw, load_firmware, init_hw) after video_unregister_device(), DMA teardown and s5p_mfc_final_pm() have run, a potential use-after-free.

Use timer_shutdown_sync(), which puts the timer into a shutdown state so that any add_timer()/mod_timer() from the callback becomes a no-op and no later firing is possible. Switch flush_work() to cancel_work_sync() so any watchdog_work that was already queued before the timer was stopped is cancelled rather than allowed to run to completion against the torn-down device.

This issue was found by an in-house static analysis tool. No runtime reproducer is available.

---
 drivers/media/platform/samsung/s5p-mfc/s5p_mfc.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

index e30e54935d79a..1386208b092f5 100644
@@ -1454,8 +1454,8 @@ static void s5p_mfc_remove(struct platform_device *pdev)
 	}
 	mutex_unlock(&dev->mfc_mutex);
 
-	del_timer_sync(&dev->watchdog_timer);
-	flush_work(&dev->watchdog_work);
+	timer_shutdown_sync(&dev->watchdog_timer);
+	cancel_work_sync(&dev->watchdog_work);
 
 	video_unregister_device(dev->vfd_enc);
 	video_unregister_device(dev->vfd_dec);

2.53.0