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block: bdrv_inactivate_recurse(): check for permissions and fix crash
authorVladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Sat, 11 Sep 2021 12:00:27 +0000 (15:00 +0300)
committerHanna Reitz <hreitz@redhat.com>
Wed, 15 Sep 2021 13:54:07 +0000 (15:54 +0200)
commita13de40a05478e64726dd9861135d344837f3c30
tree9472d3026cffb723b7f8668f337fd09e21a59ab3
parent2f43482733352e4423fcbddadd09265de92ddf58
block: bdrv_inactivate_recurse(): check for permissions and fix crash

We must not inactivate child when parent has write permissions on
it.

Calling .bdrv_inactivate() doesn't help: actually only qcow2 has this
handler and it is used to flush caches, not for permission
manipulations.

So, let's simply check cumulative parent permissions before
inactivating the node.

This commit fixes a crash when we do migration during backup: prior to
the commit nothing prevents all nodes inactivation at migration finish
and following backup write to the target crashes on assertion
"assert(!(bs->open_flags & BDRV_O_INACTIVE));" in
bdrv_co_write_req_prepare().

After the commit, we rely on the fact that copy-before-write filter
keeps write permission on target node to be able to write to it. So
inactivation fails and migration fails as expected.

Corresponding test now passes, so, enable it.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: Hanna Reitz <hreitz@redhat.com>
Message-Id: <20210911120027.8063-3-vsementsov@virtuozzo.com>
Signed-off-by: Hanna Reitz <hreitz@redhat.com>
block.c
tests/qemu-iotests/tests/migrate-during-backup