[3.13.y.z extended stable] Patch "md/raid1: be more cautious where we read-balance during resync." has been added to staging queue

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    md/raid1:  be more cautious where we read-balance during resync.

to the linux-3.13.y-queue branch of the 3.13.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.13.y-queue

This patch is scheduled to be released in version 3.13.11.9.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.13.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From a00a33082b97a0cc19669f09c51a6e26e0c6857f Mon Sep 17 00:00:00 2001
From: NeilBrown <neilb at suse.de>
Date: Tue, 9 Sep 2014 13:49:46 +1000
Subject: md/raid1:  be more cautious where we read-balance during resync.

commit c6d119cf1b5a778e9ed60a006e2a434fcc4471a2 upstream.

commit 79ef3a8aa1cb1523cc231c9a90a278333c21f761 made
it possible for reads to happen concurrently with resync.
This means that we need to be more careful where read_balancing
is allowed during resync - we can no longer be sure that any
resync that has already started will definitely finish.

So keep read_balancing to before recovery_cp, which is conservative
but safe.

This bug makes it possible to read from a device that doesn't
have up-to-date data, so it can cause data corruption.
So it is suitable for any kernel since 3.11.

Fixes: 79ef3a8aa1cb1523cc231c9a90a278333c21f761
Signed-off-by: NeilBrown <neilb at suse.de>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 drivers/md/raid1.c | 6 +-----
 1 file changed, 1 insertion(+), 5 deletions(-)

diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
index b806da4..e124f01 100644
--- a/drivers/md/raid1.c
+++ b/drivers/md/raid1.c
@@ -542,11 +542,7 @@ static int read_balance(struct r1conf *conf, struct r1bio *r1_bio, int *max_sect
 	has_nonrot_disk = 0;
 	choose_next_idle = 0;

-	if (conf->mddev->recovery_cp < MaxSector &&
-	    (this_sector + sectors >= conf->next_resync))
-		choose_first = 1;
-	else
-		choose_first = 0;
+	choose_first = (conf->mddev->recovery_cp < this_sector + sectors);

 	for (disk = 0 ; disk < conf->raid_disks * 2 ; disk++) {
 		sector_t dist;
--
1.9.1