md: always clear ->safemode when md_check_recovery gets the mddev lock.

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.

Fixes: 4ad23a976413 ("MD: use per-cpu counter for writes_pending")
Cc: stable@vger.kernel.org (4.12+)
Reported-by: Dominik Brodowski <linux@dominikbrodowski.net>
Reported-by: David R <david@unsolicited.net>
Signed-off-by: NeilBrown <neilb@suse.com>
Signed-off-by: Shaohua Li <shli@fb.com>

diff --git a/drivers/md/md.c b/drivers/md/md.c
index c99634612fc408fbc97df9c7c8ef8e028efe2fad..d84aceede1cbcc9706b339e996462f5cadddb7b8 100644 (file)
--- 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)