md raid: fix hang when stopping arrays with metadata through dm-raid

When using device-mapper's dm-raid target, stopping a RAID array can cause
the system to hang under specific conditions.

This occurs when:

- A dm-raid managed device tree is suspended from top to bottom
   (the top-level RAID device is suspended first, followed by its
    underlying metadata and data devices)

- The top-level RAID device is then removed

Removing the top-level device triggers a hang in the following sequence:
the dm-raid destructor calls md_stop(), which tries to flush the
write-intent bitmap by writing to the metadata sub-devices. However, these
devices are already suspended, making them unable to complete the write-intent
operations and causing an indefinite block.

Fix:

- Prevent bitmap flushing when md_stop() is called from dm-raid
destructor context
  and avoid a quiescing/unquescing cycle which could also cause I/O

- Still allow write-intent bitmap flushing when called from dm-raid
suspend context

This ensures that RAID array teardown can complete successfully even when the
underlying devices are in a suspended state.

This second patch uses md_is_rdwr() to distinguish between suspend and
destructor paths as elaborated on above.

Link: https://lore.kernel.org/linux-raid/CAM23VxqYrwkhKEBeQrZeZwQudbiNey2_8B_SEOLqug=pXxaFrA@mail.gmail.com
Signed-off-by: Heinz Mauelshagen <heinzm@redhat.com>
Signed-off-by: Yu Kuai <yukuai@fnnas.com>

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 606f616190d77f8432920b14981ccc59b7ab5f2d..59cd303548de8e4cda0fcca2334340bf4ebd9bd3 100644 (file)
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -6851,13 +6851,15 @@ static void __md_stop_writes(struct mddev *mddev)
 {
        timer_delete_sync(&mddev->safemode_timer);
 
-       if (mddev->pers && mddev->pers->quiesce) {
-               mddev->pers->quiesce(mddev, 1);
-               mddev->pers->quiesce(mddev, 0);
-       }
+       if (md_is_rdwr(mddev) || !mddev_is_dm(mddev)) {
+               if (mddev->pers && mddev->pers->quiesce) {
+                       mddev->pers->quiesce(mddev, 1);
+                       mddev->pers->quiesce(mddev, 0);
+               }
 
-       if (md_bitmap_enabled(mddev, true))
-               mddev->bitmap_ops->flush(mddev);
+               if (md_bitmap_enabled(mddev, true))
+                       mddev->bitmap_ops->flush(mddev);
+       }
 
        if (md_is_rdwr(mddev) &&
            ((!mddev->in_sync && !mddev_is_clustered(mddev)) ||