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

The hang happens because removing the top-level device triggers md_stop() from the
dm-raid destructor.  This function attempts to flush the write-intent bitmap, which
requires writing bitmap superblocks to the metadata sub-devices.  However, since
these metadata devices are already suspended, the write operations cannot complete,
causing the system to hang.

Fix:

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

-  Avoid any I/O operations that might occur during the quiesce/unquiesce process in md_stop()

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

Signed-off-by: Heinz Mauelshagen <heinzm@redhat.com>
---
 drivers/md/md.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 4e033c26fdd4..53e15bdd9ab2 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -6541,12 +6541,14 @@ 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 (!mddev_is_dm(mddev)) {
+		if (mddev->pers && mddev->pers->quiesce) {
+			mddev->pers->quiesce(mddev, 1);
+			mddev->pers->quiesce(mddev, 0);
+		}
 
-	mddev->bitmap_ops->flush(mddev);
+		mddev->bitmap_ops->flush(mddev);
+	}
 
 	if (md_is_rdwr(mddev) &&
 	    ((!mddev->in_sync && !mddev_is_clustered(mddev)) ||
-- 
2.51.0

Hi,

在 2025/09/18 21:42, Heinz Mauelshagen 写道:
> 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
> 
> The hang happens because removing the top-level device triggers md_stop() from the
> dm-raid destructor.  This function attempts to flush the write-intent bitmap, which
> requires writing bitmap superblocks to the metadata sub-devices.  However, since
> these metadata devices are already suspended, the write operations cannot complete,
> causing the system to hang.
> 
> Fix:
> 
> -  Prevent bitmap flushing when md_stop() is called from dm-raid contexts
>     and avoid a quiescing/unquescing cycle which could also cause I/O

If bitmap flush is skipped, then bitmap can still be dirty after dm-raid
is stopped, and the next time when dm-raid is reloaded, looks like there
will be unnecessary data resync because there are dirty bits?

Thanks,
Kuai

> 
> -  Avoid any I/O operations that might occur during the quiesce/unquiesce process in md_stop()
> 
> This ensures that RAID array teardown can complete successfully even when the
> underlying devices are in a suspended state.
> 
> Signed-off-by: Heinz Mauelshagen <heinzm@redhat.com>
> ---
>   drivers/md/md.c | 12 +++++++-----
>   1 file changed, 7 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/md/md.c b/drivers/md/md.c
> index 4e033c26fdd4..53e15bdd9ab2 100644
> --- a/drivers/md/md.c
> +++ b/drivers/md/md.c
> @@ -6541,12 +6541,14 @@ 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 (!mddev_is_dm(mddev)) {
> +		if (mddev->pers && mddev->pers->quiesce) {
> +			mddev->pers->quiesce(mddev, 1);
> +			mddev->pers->quiesce(mddev, 0);
> +		}
>   
> -	mddev->bitmap_ops->flush(mddev);
> +		mddev->bitmap_ops->flush(mddev);
> +	}
>   
>   	if (md_is_rdwr(mddev) &&
>   	    ((!mddev->in_sync && !mddev_is_clustered(mddev)) ||
>