linux-kernel - [PATCH 4.12 10/41] md: always clear ->safemode when md_check

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Message-Id: <20170822190942.325317697@linuxfoundation.org>
Date:   Tue, 22 Aug 2017 12:13:38 -0700
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        Dominik Brodowski <linux@...inikbrodowski.net>,
        David R <david@...olicited.net>, NeilBrown <neilb@...e.com>,
        Shaohua Li <shli@...com>
Subject: [PATCH 4.12 10/41] md: always clear ->safemode when md_check_recovery gets the mddev lock.

4.12-stable review patch.  If anyone has any objections, please let me know.

------------------

From: NeilBrown <neilb@...e.com>

commit 33182d15c6bf182f7ae32a66ea4a547d979cd6d7 upstream.

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")
Reported-by: Dominik Brodowski <linux@...inikbrodowski.net>
Reported-by: David R <david@...olicited.net>
Signed-off-by: NeilBrown <neilb@...e.com>
Signed-off-by: Shaohua Li <shli@...com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/md/md.c |    3 +++
 1 file changed, 3 insertions(+)

--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -8639,6 +8639,9 @@ void md_check_recovery(struct mddev *mdd
 	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)