[PATCH v2 0/2] fix crash if try to migrate during backup

[PATCH v2 0/2] fix crash if try to migrate during backup

[Vladimir Sementsov-Ogievskiy]

v2:
01: check that migration fails
02: Add Hanna's r-b

Vladimir Sementsov-Ogievskiy (2):
  tests: add migrate-during-backup
  block: bdrv_inactivate_recurse(): check for permissions and fix crash

 block.c                                       |  8 ++
 .../qemu-iotests/tests/migrate-during-backup  | 97 +++++++++++++++++++
 .../tests/migrate-during-backup.out           |  5 +
 3 files changed, 110 insertions(+)
 create mode 100755 tests/qemu-iotests/tests/migrate-during-backup
 create mode 100644 tests/qemu-iotests/tests/migrate-during-backup.out

-- 
2.29.2

[PATCH v2 1/2] tests: add migrate-during-backup

[Vladimir Sementsov-Ogievskiy]

Add a simple test which tries to run migration during backup.
bdrv_inactivate_all() should fail. But due to bug (see next commit with
fix) it doesn't, nodes are inactivated and continued backup crashes
on assertion "assert(!(bs->open_flags & BDRV_O_INACTIVE));" in
bdrv_co_write_req_prepare().

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
---
 .../qemu-iotests/tests/migrate-during-backup  | 97 +++++++++++++++++++
 .../tests/migrate-during-backup.out           |  5 +
 2 files changed, 102 insertions(+)
 create mode 100755 tests/qemu-iotests/tests/migrate-during-backup
 create mode 100644 tests/qemu-iotests/tests/migrate-during-backup.out

diff --git a/tests/qemu-iotests/tests/migrate-during-backup b/tests/qemu-iotests/tests/migrate-during-backup
new file mode 100755
index 0000000000..1046904c5a
--- /dev/null
+++ b/tests/qemu-iotests/tests/migrate-during-backup
@@ -0,0 +1,97 @@
+#!/usr/bin/env python3
+# group: migration disabled
+#
+# Copyright (c) 2021 Virtuozzo International GmbH
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+#
+
+import os
+import iotests
+from iotests import qemu_img_create, qemu_io
+
+
+disk_a = os.path.join(iotests.test_dir, 'disk_a')
+disk_b = os.path.join(iotests.test_dir, 'disk_b')
+size = '1M'
+mig_file = os.path.join(iotests.test_dir, 'mig_file')
+mig_cmd = 'exec: cat > ' + mig_file
+
+
+class TestMigrateDuringBackup(iotests.QMPTestCase):
+    def tearDown(self):
+        self.vm.shutdown()
+        os.remove(disk_a)
+        os.remove(disk_b)
+        os.remove(mig_file)
+
+    def setUp(self):
+        qemu_img_create('-f', iotests.imgfmt, disk_a, size)
+        qemu_img_create('-f', iotests.imgfmt, disk_b, size)
+        qemu_io('-c', f'write 0 {size}', disk_a)
+
+        self.vm = iotests.VM().add_drive(disk_a)
+        self.vm.launch()
+        result = self.vm.qmp('blockdev-add', {
+            'node-name': 'target',
+            'driver': iotests.imgfmt,
+            'file': {
+                'driver': 'file',
+                'filename': disk_b
+            }
+        })
+        self.assert_qmp(result, 'return', {})
+
+    def test_migrate(self):
+        result = self.vm.qmp('blockdev-backup', device='drive0',
+                             target='target', sync='full',
+                             speed=1, x_perf={
+                                 'max-workers': 1,
+                                 'max-chunk': 64 * 1024
+                             })
+        self.assert_qmp(result, 'return', {})
+
+        result = self.vm.qmp('job-pause', id='drive0')
+        self.assert_qmp(result, 'return', {})
+
+        result = self.vm.qmp('migrate-set-capabilities',
+                             capabilities=[{'capability': 'events',
+                                            'state': True}])
+        self.assert_qmp(result, 'return', {})
+        result = self.vm.qmp('migrate', uri=mig_cmd)
+        self.assert_qmp(result, 'return', {})
+
+        e = self.vm.events_wait((('MIGRATION',
+                                  {'data': {'status': 'completed'}}),
+                                 ('MIGRATION',
+                                  {'data': {'status': 'failed'}})))
+
+        # Don't assert that e is 'failed' now: this way we'll miss
+        # possible crash when backup continues :)
+
+        result = self.vm.qmp('block-job-set-speed', device='drive0',
+                             speed=0)
+        self.assert_qmp(result, 'return', {})
+        result = self.vm.qmp('job-resume', id='drive0')
+        self.assert_qmp(result, 'return', {})
+
+        # For future: if something changes so that both migration
+        # and backup pass, let's not miss that moment, as it may
+        # be a bug as well as improvement.
+        self.assert_qmp(e, 'data/status', 'failed')
+
+
+if __name__ == '__main__':
+    iotests.main(supported_fmts=['qcow2'],
+                 supported_protocols=['file'])
diff --git a/tests/qemu-iotests/tests/migrate-during-backup.out b/tests/qemu-iotests/tests/migrate-during-backup.out
new file mode 100644
index 0000000000..ae1213e6f8
--- /dev/null
+++ b/tests/qemu-iotests/tests/migrate-during-backup.out
@@ -0,0 +1,5 @@
+.
+----------------------------------------------------------------------
+Ran 1 tests
+
+OK
-- 
2.29.2

[PATCH v2 2/2] block: bdrv_inactivate_recurse(): check for permissions and fix crash

[Vladimir Sementsov-Ogievskiy]

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>
---
 block.c                                        | 8 ++++++++
 tests/qemu-iotests/tests/migrate-during-backup | 2 +-
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/block.c b/block.c
index b2b66263f9..ceb2b66afc 100644
--- a/block.c
+++ b/block.c
@@ -6319,6 +6319,7 @@ static int bdrv_inactivate_recurse(BlockDriverState *bs)
 {
     BdrvChild *child, *parent;
     int ret;
+    uint64_t cumulative_perms, cumulative_shared_perms;
 
     if (!bs->drv) {
         return -ENOMEDIUM;
@@ -6349,6 +6350,13 @@ static int bdrv_inactivate_recurse(BlockDriverState *bs)
         }
     }
 
+    bdrv_get_cumulative_perm(bs, &cumulative_perms,
+                             &cumulative_shared_perms);
+    if (cumulative_perms & (BLK_PERM_WRITE | BLK_PERM_WRITE_UNCHANGED)) {
+        /* Our inactive parents still need write access. Inactivation failed. */
+        return -EPERM;
+    }
+
     bs->open_flags |= BDRV_O_INACTIVE;
 
     /*
diff --git a/tests/qemu-iotests/tests/migrate-during-backup b/tests/qemu-iotests/tests/migrate-during-backup
index 1046904c5a..34103229ee 100755
--- a/tests/qemu-iotests/tests/migrate-during-backup
+++ b/tests/qemu-iotests/tests/migrate-during-backup
@@ -1,5 +1,5 @@
 #!/usr/bin/env python3
-# group: migration disabled
+# group: migration
 #
 # Copyright (c) 2021 Virtuozzo International GmbH
 #
-- 
2.29.2

Re: [PATCH v2 0/2] fix crash if try to migrate during backup

[Hanna Reitz]

On 11.09.21 14:00, Vladimir Sementsov-Ogievskiy wrote:
> v2:
> 01: check that migration fails
> 02: Add Hanna's r-b
>
> Vladimir Sementsov-Ogievskiy (2):
>    tests: add migrate-during-backup
>    block: bdrv_inactivate_recurse(): check for permissions and fix crash
>
>   block.c                                       |  8 ++
>   .../qemu-iotests/tests/migrate-during-backup  | 97 +++++++++++++++++++
>   .../tests/migrate-during-backup.out           |  5 +
>   3 files changed, 110 insertions(+)
>   create mode 100755 tests/qemu-iotests/tests/migrate-during-backup
>   create mode 100644 tests/qemu-iotests/tests/migrate-during-backup.out

Thanks, applied to my block branch:

https://github.com/XanClic/qemu/commits/block

Hanna