From 6123c29fcf385010a683061fd7f948f256713b48 Mon Sep 17 00:00:00 2001

From: Kevin Wolf <kwolf@redhat.com>

Date: Fri, 17 May 2019 14:23:15 +0100

Subject: [PATCH 4/5] block: Fix invalidate_cache error path for parent

 activation

RH-Author: Kevin Wolf <kwolf@redhat.com>

Message-id: <20190517142315.16266-2-kwolf@redhat.com>

Patchwork-id: 88024

O-Subject: [RHEL-8.1 qemu-kvm PATCH 1/1] block: Fix invalidate_cache error path for parent activation

Bugzilla: 1673010

RH-Acked-by: John Snow <jsnow@redhat.com>

RH-Acked-by: Sergio Lopez Pascual <slp@redhat.com>

RH-Acked-by: Stefano Garzarella <sgarzare@redhat.com>

bdrv_co_invalidate_cache() clears the BDRV_O_INACTIVE flag before

actually activating a node so that the correct permissions etc. are

taken. In case of errors, the flag must be restored so that the next

call to bdrv_co_invalidate_cache() retries activation.

Restoring the flag was missing in the error path for a failed

parent->role->activate() call. The consequence is that this attempt to

activate all images correctly fails because we still set errp, however

on the next attempt BDRV_O_INACTIVE is already clear, so we return

success without actually retrying the failed action.

An example where this is observable in practice is migration to a QEMU

instance that has a raw format block node attached to a guest device

with share-rw=off (the default) while another process holds

BLK_PERM_WRITE for the same image. In this case, all activation steps

before parent->role->activate() succeed because raw can tolerate other

writers to the image. Only the parent callback (in particular

blk_root_activate()) tries to implement the share-rw=on property and

requests exclusive write permissions. This fails when the migration

completes and correctly displays an error. However, a manual 'cont' will

incorrectly resume the VM without calling blk_root_activate() again.

This case is described in more detail in the following bug report:

https://bugzilla.redhat.com/show_bug.cgi?id=1531888

Fix this by correctly restoring the BDRV_O_INACTIVE flag in the error

path.

Cc: qemu-stable@nongnu.org

Signed-off-by: Kevin Wolf <kwolf@redhat.com>

Tested-by: Markus Armbruster <armbru@redhat.com>

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>

(cherry picked from commit 78fc3b3a26c145eebcdee992988644974b243a74)

Signed-off-by: Kevin Wolf <kwolf@redhat.com>

Signed-off-by: Danilo C. L. de Paula <ddepaula@redhat.com>

---

 block.c | 1 +

 1 file changed, 1 insertion(+)

diff --git a/block.c b/block.c

index d0f0dc6..82b16df 100644

--- a/block.c

+++ b/block.c

@@ -4417,6 +4417,7 @@ static void coroutine_fn bdrv_co_invalidate_cache(BlockDriverState *bs,

         if (parent->role->activate) {

             parent->role->activate(parent, &local_err);

             if (local_err) {

+                bs->open_flags |= BDRV_O_INACTIVE;

                 error_propagate(errp, local_err);

                 return;

             }

-- 

1.8.3.1