On Tue, Aug 08, 2017 at 04:56:36PM +1000, Neil Brown wrote:
> If ->safemode == 1, md_check_recovery() will try to get the mddev lock
> and perform various other checks.
> If mddev->in_sync is zero, it will call set_in_sync, and clear
> ->safemode. However if mddev->in_sync is not zero, ->safemode will not
> be cleared.
>
> When md_check_recovery() drops the mddev lock, the thread is woken
> up again. Normally it would just check if there was anything else to
> do, find nothing, and go to sleep. However as ->safemode was not
> cleared, it will take the mddev lock again, then wake itself up
> when unlocking.
>
> This results in an infinite loop, repeatedly calling
> md_check_recovery(), which RCU or the soft-lockup detector
> will eventually complain about.
>
> Prior to commit 4ad23a976413 ("MD: use per-cpu counter for
> writes_pending"), safemode would only be set to one when the
> writes_pending counter reached zero, and would be cleared again
> when writes_pending is incremented. Since that patch, safemode
> is set more freely, but is not reliably cleared.
>
> So in md_check_recovery() clear ->safemode before checking ->in_sync.
Nice catch! Applied both patches.
I spent hours to check why md_check_recovery loops, apparently I missed
set_in_sync is only called when in_sync is not set, silly me.
Thanks,
Shaohua
> Fixes: 4ad23a976413 ("MD: use per-cpu counter for writes_pending")
> Cc: stable@xxxxxxxxxxxxxxx (4.12+)
> Reported-by: Dominik Brodowski <linux@xxxxxxxxxxxxxxxxxxxx>
> Reported-by: David R <david@xxxxxxxxxxxxxxx>
> Signed-off-by: NeilBrown <neilb@xxxxxxxx>
> ---
> drivers/md/md.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/drivers/md/md.c b/drivers/md/md.c
> index c99634612fc4..d84aceede1cb 100644
> --- a/drivers/md/md.c
> +++ b/drivers/md/md.c
> @@ -8656,6 +8656,9 @@ void md_check_recovery(struct mddev *mddev)
> if (mddev_trylock(mddev)) {
> int spares = 0;
>
> + if (mddev->safemode == 1)
> + mddev->safemode = 0;
> +
> if (mddev->ro) {
> struct md_rdev *rdev;
> if (!mddev->external && mddev->in_sync)
>
>
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