[3.13.y-ckt stable] Patch "rbd: drop parent_ref in rbd_dev_unprobe() unconditionally" has been added to staging queue

[Kamal Mostafa]

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

    rbd: drop parent_ref in rbd_dev_unprobe() unconditionally

to the linux-3.13.y-queue branch of the 3.13.y-ckt 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-ckt17.

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-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From 04307d840b078b74551480030a8a085c2bc8b72c Mon Sep 17 00:00:00 2001
From: Ilya Dryomov <idryomov at redhat.com>
Date: Mon, 19 Jan 2015 12:06:14 +0300
Subject: rbd: drop parent_ref in rbd_dev_unprobe() unconditionally

commit e69b8d414f948c242ad9f3eb2b7e24fba783dbbd upstream.

This effectively reverts the last hunk of 392a9dad7e77 ("rbd: detect
when clone image is flattened").

The problem with parent_overlap != 0 condition is that it's possible
and completely valid to have an image with parent_overlap == 0 whose
parent state needs to be cleaned up on unmap.  The next commit, which
drops the "clone image now standalone" logic, opens up another window
of opportunity to hit this, but even without it

    # cat parent-ref.sh
    #!/bin/bash
    rbd create --image-format 2 --size 1 foo
    rbd snap create foo at snap
    rbd snap protect foo at snap
    rbd clone foo at snap bar
    rbd resize --allow-shrink --size 0 bar
    rbd resize --size 1 bar
    DEV=$(rbd map bar)
    rbd unmap $DEV

leaves rbd_device/rbd_spec/etc and rbd_client along with ceph_client
hanging around.

My thinking behind calling rbd_dev_parent_put() unconditionally is that
there shouldn't be any requests in flight at that point in time as we
are deep into unmap sequence.  Hence, even if rbd_dev_unparent() caused
by flatten is delayed by in-flight requests, it will have finished by
the time we reach rbd_dev_unprobe() caused by unmap, thus turning
unconditional rbd_dev_parent_put() into a no-op.

Fixes: http://tracker.ceph.com/issues/10352

Signed-off-by: Ilya Dryomov <idryomov at redhat.com>
Reviewed-by: Josh Durgin <jdurgin at redhat.com>
Reviewed-by: Alex Elder <elder at linaro.org>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 drivers/block/rbd.c | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c
index caa97de..912a068 100644
--- a/drivers/block/rbd.c
+++ b/drivers/block/rbd.c
@@ -4774,10 +4774,7 @@ static void rbd_dev_unprobe(struct rbd_device *rbd_dev)
 {
 	struct rbd_image_header	*header;

-	/* Drop parent reference unless it's already been done (or none) */
-
-	if (rbd_dev->parent_overlap)
-		rbd_dev_parent_put(rbd_dev);
+	rbd_dev_parent_put(rbd_dev);

 	/* Free dynamic fields from the header, then zero it out */

--
1.9.1