linux-kernel - [PATCH 3.16 331/357] md/raid1: make sure resync waits for conflicting writes to complete.

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Message-Id: <20141003212943.403555416@linuxfoundation.org>
Date:	Fri,  3 Oct 2014 14:31:57 -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, majianpeng <majianpeng@...il.com>,
	NeilBrown <neilb@...e.de>
Subject: [PATCH 3.16 331/357] md/raid1: make sure resync waits for conflicting writes to complete.

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

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

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

commit 2f73d3c55d09ce60647b96ad2a9b539c95a530ee upstream.

The resync/recovery process for raid1 was recently changed
so that writes could happen in parallel with resync providing
they were in different regions of the device.

There is a problem though:  While a write request will always
wait for conflicting resync to complete, a resync request
will *not* always wait for conflicting writes to complete.

Two changes are needed to fix this:

1/ raise_barrier (which waits until it is safe to do resync)
   must wait until current_window_requests is zero
2/ wait_battier (which waits at the start of a new write request)
   must update current_window_requests if the request could
   possible conflict with a concurrent resync.

As concurrent writes and resync can lead to data loss,
this patch is suitable for -stable.

Fixes: 79ef3a8aa1cb1523cc231c9a90a278333c21f761
Cc: majianpeng <majianpeng@...il.com>
Signed-off-by: NeilBrown <neilb@...e.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/md/raid1.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

--- a/drivers/md/raid1.c
+++ b/drivers/md/raid1.c
@@ -845,10 +845,12 @@ static void raise_barrier(struct r1conf
 	 * C: next_resync + RESYNC_SECTORS > start_next_window, meaning
 	 *    next resync will reach to the window which normal bios are
 	 *    handling.
+	 * D: while there are any active requests in the current window.
 	 */
 	wait_event_lock_irq(conf->wait_barrier,
 			    !conf->array_frozen &&
 			    conf->barrier < RESYNC_DEPTH &&
+			    conf->current_window_requests == 0 &&
 			    (conf->start_next_window >=
 			     conf->next_resync + RESYNC_SECTORS),
 			    conf->resync_lock);
@@ -915,8 +917,8 @@ static sector_t wait_barrier(struct r1co
 	}
 
 	if (bio && bio_data_dir(bio) == WRITE) {
-		if (conf->next_resync + NEXT_NORMALIO_DISTANCE
-		    <= bio->bi_iter.bi_sector) {
+		if (bio->bi_iter.bi_sector >=
+		    conf->next_resync) {
 			if (conf->start_next_window == MaxSector)
 				conf->start_next_window =
 					conf->next_resync +


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