On Sun, Jul 31 2016, shli@xxxxxxxxxx wrote:
> From: Shaohua Li <shli@xxxxxx>
>
> .quiesce is called with mddev lock hold at most places. There are few
> exceptions. Calling .quesce without the lock hold could create races. For
> example, the .quesce of raid1 can't be recursively. The purpose of the patches
> is to fix a race in raid5-cache. The raid5-cache .quesce will write md
> superblock and should be called with mddev lock hold.
>
> Cc: NeilBrown <neilb@xxxxxxxx>
> Signed-off-by: Shaohua Li <shli@xxxxxx>
Acked-by: NeilBrown <neilb@xxxxxxxx>
This should be safe but I'm not sure I really like it.
The raid1 quiesce could be changed so that it can be called recursively.
The raid5-cache situation would be harder to get right and maybe this is
the best solution... It's just that 'quiesce' should be a fairly
light-weight operation, just waiting for pending requests to flush. It
shouldn't really *need* a lock.
NeilBrown
> ---
> drivers/md/md.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/drivers/md/md.c b/drivers/md/md.c
> index 2c3ab6f..0550445 100644
> --- a/drivers/md/md.c
> +++ b/drivers/md/md.c
> @@ -7945,8 +7945,10 @@ void md_do_sync(struct md_thread *thread)
> * region.
> */
> if (mddev->bitmap) {
> + mddev_lock_nointr(mddev);
> mddev->pers->quiesce(mddev, 1);
> mddev->pers->quiesce(mddev, 0);
> + mddev_unlock(mddev);
> }
> }
>
> --
> 2.7.4
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