Patch "raid1: prevent freeze_array/wait_all_barriers deadlock" has been added to the 4.14-stable tree

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

    raid1: prevent freeze_array/wait_all_barriers deadlock

to the 4.14-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     raid1-prevent-freeze_array-wait_all_barriers-deadlock.patch
and it can be found in the queue-4.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From f6eca2d43ed694ab8124dd24c88277f7eca93b7d Mon Sep 17 00:00:00 2001
From: Nate Dailey <nate.dailey@stratus.com>
Date: Tue, 17 Oct 2017 08:17:03 -0400
Subject: raid1: prevent freeze_array/wait_all_barriers deadlock

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


Patches currently in stable-queue which might be from nate.dailey@stratus.com are

queue-4.14/raid1-prevent-freeze_array-wait_all_barriers-deadlock.patch