linux-kernel - [PATCH 4.14 128/193] raid1: prevent freeze_array/wait_all

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Message-Id: <20171128100619.303923847@linuxfoundation.org>
Date:   Tue, 28 Nov 2017 11:26:15 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Nate Dailey <nate.dailey@...atus.com>,
        Coly Li <colyli@...e.de>, Shaohua Li <shli@...com>
Subject: [PATCH 4.14 128/193] raid1: prevent freeze_array/wait_all_barriers deadlock

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

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

From: Nate Dailey <nate.dailey@...atus.com>

commit f6eca2d43ed694ab8124dd24c88277f7eca93b7d upstream.

If freeze_array is attempted in the middle of close_sync/
wait_all_barriers, deadlock can occur.

freeze_array will wait for nr_pending and nr_queued to line up.
wait_all_barriers increments nr_pending for each barrier bucket, one
at a time, but doesn't actually issue IO that could be counted in
nr_queued. So freeze_array is blocked until wait_all_barriers
completes and allow_all_barriers runs. At the same time, when
_wait_barrier sees array_frozen == 1, it stops and waits for
freeze_array to complete.

Prevent the deadlock by making close_sync call _wait_barrier and
_allow_barrier for one bucket at a time, instead of deferring the
_allow_barrier calls until after all _wait_barriers are complete.

Signed-off-by: Nate Dailey <nate.dailey@...atus.com>
Fix: fd76863e37fe(RAID1: a new I/O barrier implementation to remove resync window)
Reviewed-by: Coly Li <colyli@...e.de>
Signed-off-by: Shaohua Li <shli@...com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/md/raid1.c |   24 ++++++------------------
 1 file changed, 6 insertions(+), 18 deletions(-)

--- a/drivers/md/raid1.c
+++ b/drivers/md/raid1.c
@@ -990,14 +990,6 @@ static void wait_barrier(struct r1conf *
 	_wait_barrier(conf, idx);
 }
 
-static void wait_all_barriers(struct r1conf *conf)
-{
-	int idx;
-
-	for (idx = 0; idx < BARRIER_BUCKETS_NR; idx++)
-		_wait_barrier(conf, idx);
-}
-
 static void _allow_barrier(struct r1conf *conf, int idx)
 {
 	atomic_dec(&conf->nr_pending[idx]);
@@ -1011,14 +1003,6 @@ static void allow_barrier(struct r1conf
 	_allow_barrier(conf, idx);
 }
 
-static void allow_all_barriers(struct r1conf *conf)
-{
-	int idx;
-
-	for (idx = 0; idx < BARRIER_BUCKETS_NR; idx++)
-		_allow_barrier(conf, idx);
-}
-
 /* conf->resync_lock should be held */
 static int get_unqueued_pending(struct r1conf *conf)
 {
@@ -1654,8 +1638,12 @@ static void print_conf(struct r1conf *co
 
 static void close_sync(struct r1conf *conf)
 {
-	wait_all_barriers(conf);
-	allow_all_barriers(conf);
+	int idx;
+
+	for (idx = 0; idx < BARRIER_BUCKETS_NR; idx++) {
+		_wait_barrier(conf, idx);
+		_allow_barrier(conf, idx);
+	}
 
 	mempool_destroy(conf->r1buf_pool);
 	conf->r1buf_pool = NULL;