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