[4.2.y-ckt stable] Patch "md: remove check for MD_RECOVERY_NEEDED in action_store." has been added to the 4.2.y-ckt tree

[Kamal Mostafa]

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

    md: remove check for MD_RECOVERY_NEEDED in action_store.

to the linux-4.2.y-queue branch of the 4.2.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-4.2.y-queue

This patch is scheduled to be released in version 4.2.8-ckt2.

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

For more information about the 4.2.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

---8<------------------------------------------------------------

>From 00bef3ea5bb33428b0e4e7d18ce7acf43dec38b7 Mon Sep 17 00:00:00 2001
From: NeilBrown <neilb at suse.com>
Date: Mon, 21 Dec 2015 11:01:21 +1100
Subject: md: remove check for MD_RECOVERY_NEEDED in action_store.

commit 312045eef985b61d74c28047ecd8eca6719d9516 upstream.

md currently doesn't allow a 'sync_action' such as 'reshape' to be set
while MD_RECOVERY_NEEDED is set.

This s a problem, particularly since commit 738a273806ee as that can
cause ->check_shape to call mddev_resume() which sets
MD_RECOVERY_NEEDED.  So by the time we come to start 'reshape' it is
very likely that MD_RECOVERY_NEEDED is still set.

Testing for this flag is not really needed and is in any case very
racy as it can be set at any moment - asynchronously.  Any race
between setting a sync_action and setting MD_RECOVERY_NEEDED must
already be handled properly in some locked code, probably
md_check_recovery(), so remove the test here.

The test on MD_RECOVERY_RUNNING is also racy in the 'reshape' case
so we should test it again after getting mddev_lock().

As this fixes a race and a regression which can cause 'reshape' to
fail, it is suitable for -stable kernels since 4.1

Reported-by: Xiao Ni <xni at redhat.com>
Fixes: 738a273806ee ("md/raid5: fix allocation of 'scribble' array.")
Signed-off-by: NeilBrown <neilb at suse.com>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 drivers/md/md.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 95e7b72..3d49672 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -4235,8 +4235,7 @@ action_store(struct mddev *mddev, const char *page, size_t len)
 			}
 			mddev_unlock(mddev);
 		}
-	} else if (test_bit(MD_RECOVERY_RUNNING, &mddev->recovery) ||
-		   test_bit(MD_RECOVERY_NEEDED, &mddev->recovery))
+	} else if (test_bit(MD_RECOVERY_RUNNING, &mddev->recovery))
 		return -EBUSY;
 	else if (cmd_match(page, "resync"))
 		clear_bit(MD_RECOVERY_FROZEN, &mddev->recovery);
@@ -4249,8 +4248,12 @@ action_store(struct mddev *mddev, const char *page, size_t len)
 			return -EINVAL;
 		err = mddev_lock(mddev);
 		if (!err) {
-			clear_bit(MD_RECOVERY_FROZEN, &mddev->recovery);
-			err = mddev->pers->start_reshape(mddev);
+			if (test_bit(MD_RECOVERY_RUNNING, &mddev->recovery))
+				err =  -EBUSY;
+			else {
+				clear_bit(MD_RECOVERY_FROZEN, &mddev->recovery);
+				err = mddev->pers->start_reshape(mddev);
+			}
 			mddev_unlock(mddev);
 		}
 		if (err)
--
1.9.1