[PATCH for-4.2 0/2] Fix bitmap migration

[PATCH for-4.2 0/2] Fix bitmap migration

[Vladimir Sementsov-Ogievskiy]

Hi all!

We've faced a bug in rhev-2.12.0-33.el7-based Qemu.
In upstream, bug introduced in 4.0 by 74da6b943565c45
"block/dirty-bitmaps: implement inconsistent bit" commit.
At this commit we started to load inconsistent bitmap instead of
silently ignoring them, and it now I see that it breaks migration.

The fix is very simple, so I think it's OK for 4.2.. Still, it's not a
degradation, so we may postpone it to 5.0.

Vladimir Sementsov-Ogievskiy (2):
  block/qcow2-bitmap: fix bitmap migration
  iotests: add new test cases to bitmap migration

 block/qcow2-bitmap.c       | 21 ++++++++++++++++++++-
 tests/qemu-iotests/169     | 22 +++++++++++++++-------
 tests/qemu-iotests/169.out |  4 ++--
 3 files changed, 37 insertions(+), 10 deletions(-)

-- 
2.21.0

[PATCH 1/2] block/qcow2-bitmap: fix bitmap migration

[Vladimir Sementsov-Ogievskiy]

Fix bitmap migration with dirty-bitmaps capability enabled and shared
storage. We should ignore IN_USE bitmaps in the image on target, when
migrating bitmaps through migration channel, see new comment below.

Fixes: 74da6b943565c451
Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
---
 block/qcow2-bitmap.c | 21 ++++++++++++++++++++-
 1 file changed, 20 insertions(+), 1 deletion(-)

diff --git a/block/qcow2-bitmap.c b/block/qcow2-bitmap.c
index 809bbc5d20..8abaf632fc 100644
--- a/block/qcow2-bitmap.c
+++ b/block/qcow2-bitmap.c
@@ -988,7 +988,26 @@ bool qcow2_load_dirty_bitmaps(BlockDriverState *bs, Error **errp)
     }
 
     QSIMPLEQ_FOREACH(bm, bm_list, entry) {
-        BdrvDirtyBitmap *bitmap = load_bitmap(bs, bm, errp);
+        BdrvDirtyBitmap *bitmap;
+
+        if ((bm->flags & BME_FLAG_IN_USE) &&
+            bdrv_find_dirty_bitmap(bs, bm->name))
+        {
+            /*
+             * We already have corresponding BdrvDirtyBitmap, and bitmap in the
+             * image is marked IN_USE. Firstly, this state is valid, no reason
+             * to consider existing BdrvDirtyBitmap to be bad. Secondly it's
+             * absolutely possible, when we do migration with shared storage
+             * with dirty-bitmaps capability enabled: if the bitmap was loaded
+             * from this storage before migration start, the storage will
+             * of-course contain IN_USE outdated version of the bitmap, and we
+             * should not load it on migration target, as we already have this
+             * bitmap, being migrated.
+             */
+            continue;
+        }
+
+        bitmap = load_bitmap(bs, bm, errp);
         if (bitmap == NULL) {
             goto fail;
         }
-- 
2.21.0

[PATCH 2/2] iotests: add new test cases to bitmap migration

[Vladimir Sementsov-Ogievskiy]

Add optional pre-shutdown: shutdown/launch vm before migration. This
leads to storing persistent bitmap to the storage, which breaks
migration with dirty-bitmaps capability enabled and shared storage
until fixed by previous commit.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
---
 tests/qemu-iotests/169     | 22 +++++++++++++++-------
 tests/qemu-iotests/169.out |  4 ++--
 2 files changed, 17 insertions(+), 9 deletions(-)

diff --git a/tests/qemu-iotests/169 b/tests/qemu-iotests/169
index 8c204caf20..9656a7f620 100755
--- a/tests/qemu-iotests/169
+++ b/tests/qemu-iotests/169
@@ -134,7 +134,7 @@ class TestDirtyBitmapMigration(iotests.QMPTestCase):
         self.check_bitmap(self.vm_a, sha256 if persistent else False)
 
     def do_test_migration(self, persistent, migrate_bitmaps, online,
-                          shared_storage):
+                          shared_storage, pre_shutdown):
         granularity = 512
 
         # regions = ((start, count), ...)
@@ -142,15 +142,13 @@ class TestDirtyBitmapMigration(iotests.QMPTestCase):
                    (0xf0000, 0x10000),
                    (0xa0201, 0x1000))
 
-        should_migrate = migrate_bitmaps or persistent and shared_storage
+        should_migrate = \
+            (migrate_bitmaps and (persistent or not pre_shutdown)) or \
+            (persistent and shared_storage)
         mig_caps = [{'capability': 'events', 'state': True}]
         if migrate_bitmaps:
             mig_caps.append({'capability': 'dirty-bitmaps', 'state': True})
 
-        result = self.vm_a.qmp('migrate-set-capabilities',
-                               capabilities=mig_caps)
-        self.assert_qmp(result, 'return', {})
-
         self.vm_b.add_incoming(incoming_cmd if online else "defer")
         self.vm_b.add_drive(disk_a if shared_storage else disk_b)
 
@@ -166,6 +164,14 @@ class TestDirtyBitmapMigration(iotests.QMPTestCase):
             self.vm_a.hmp_qemu_io('drive0', 'write %d %d' % r)
         sha256 = self.get_bitmap_hash(self.vm_a)
 
+        if pre_shutdown:
+            self.vm_a.shutdown()
+            self.vm_a.launch()
+
+        result = self.vm_a.qmp('migrate-set-capabilities',
+                               capabilities=mig_caps)
+        self.assert_qmp(result, 'return', {})
+
         result = self.vm_a.qmp('migrate', uri=mig_cmd)
         while True:
             event = self.vm_a.event_wait('MIGRATION')
@@ -210,11 +216,13 @@ def inject_test_case(klass, name, method, *args, **kwargs):
     mc = operator.methodcaller(method, *args, **kwargs)
     setattr(klass, 'test_' + method + name, lambda self: mc(self))
 
-for cmb in list(itertools.product((True, False), repeat=4)):
+for cmb in list(itertools.product((True, False), repeat=5)):
     name = ('_' if cmb[0] else '_not_') + 'persistent_'
     name += ('_' if cmb[1] else '_not_') + 'migbitmap_'
     name += '_online' if cmb[2] else '_offline'
     name += '_shared' if cmb[3] else '_nonshared'
+    if (cmb[4]):
+        name += '__pre_shutdown'
 
     inject_test_case(TestDirtyBitmapMigration, name, 'do_test_migration',
                      *list(cmb))
diff --git a/tests/qemu-iotests/169.out b/tests/qemu-iotests/169.out
index 3a89159833..5c26d15c0d 100644
--- a/tests/qemu-iotests/169.out
+++ b/tests/qemu-iotests/169.out
@@ -1,5 +1,5 @@
-....................
+....................................
 ----------------------------------------------------------------------
-Ran 20 tests
+Ran 36 tests
 
 OK
-- 
2.21.0

Re: [PATCH for-4.2 0/2] Fix bitmap migration

[Max Reitz]

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On 25.11.19 13:52, Vladimir Sementsov-Ogievskiy wrote:
> Hi all!
> 
> We've faced a bug in rhev-2.12.0-33.el7-based Qemu.
> In upstream, bug introduced in 4.0 by 74da6b943565c45
> "block/dirty-bitmaps: implement inconsistent bit" commit.
> At this commit we started to load inconsistent bitmap instead of
> silently ignoring them, and it now I see that it breaks migration.
> 
> The fix is very simple, so I think it's OK for 4.2.. Still, it's not a
> degradation, so we may postpone it to 5.0.
> 
> Vladimir Sementsov-Ogievskiy (2):
>   block/qcow2-bitmap: fix bitmap migration
>   iotests: add new test cases to bitmap migration
> 
>  block/qcow2-bitmap.c       | 21 ++++++++++++++++++++-
>  tests/qemu-iotests/169     | 22 +++++++++++++++-------
>  tests/qemu-iotests/169.out |  4 ++--
>  3 files changed, 37 insertions(+), 10 deletions(-)

Reviewed-by: Max Reitz <mreitz@redhat.com>

Makes sense to me to put this into 4.2, but I don’t think it would
survive Peter’s check list. :?

(https://lists.nongnu.org/archive/html/qemu-block/2019-11/msg00807.html)

Max


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Re: [PATCH for-4.2 0/2] Fix bitmap migration

[Vladimir Sementsov-Ogievskiy]

25.11.2019 16:50, Max Reitz wrote:
> On 25.11.19 13:52, Vladimir Sementsov-Ogievskiy wrote:
>> Hi all!
>>
>> We've faced a bug in rhev-2.12.0-33.el7-based Qemu.
>> In upstream, bug introduced in 4.0 by 74da6b943565c45
>> "block/dirty-bitmaps: implement inconsistent bit" commit.
>> At this commit we started to load inconsistent bitmap instead of
>> silently ignoring them, and it now I see that it breaks migration.
>>
>> The fix is very simple, so I think it's OK for 4.2.. Still, it's not a
>> degradation, so we may postpone it to 5.0.
>>
>> Vladimir Sementsov-Ogievskiy (2):
>>    block/qcow2-bitmap: fix bitmap migration
>>    iotests: add new test cases to bitmap migration
>>
>>   block/qcow2-bitmap.c       | 21 ++++++++++++++++++++-
>>   tests/qemu-iotests/169     | 22 +++++++++++++++-------
>>   tests/qemu-iotests/169.out |  4 ++--
>>   3 files changed, 37 insertions(+), 10 deletions(-)
> 
> Reviewed-by: Max Reitz <mreitz@redhat.com>
> 
> Makes sense to me to put this into 4.2, but I don’t think it would
> survive Peter’s check list. :?

It depends on how much the fixed case is popular..

Actually, anyone who tries to migrate bitmaps with dirty-bitmaps capability
enabled and with shared storage will very possibly run into this bug.

But who is it, except for Virtuozzo, I don't know:) Still, I see that a lot
of that staff merged into Rhel Qemu we based on, so at least this should go
to qemu-stable and to Rhel update.

> 
> (https://lists.nongnu.org/archive/html/qemu-block/2019-11/msg00807.html)
> 
> Max
> 


-- 
Best regards,
Vladimir

Re: [PATCH for-4.2 0/2] Fix bitmap migration

[Max Reitz]

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On 25.11.19 13:52, Vladimir Sementsov-Ogievskiy wrote:
> Hi all!
> 
> We've faced a bug in rhev-2.12.0-33.el7-based Qemu.
> In upstream, bug introduced in 4.0 by 74da6b943565c45
> "block/dirty-bitmaps: implement inconsistent bit" commit.
> At this commit we started to load inconsistent bitmap instead of
> silently ignoring them, and it now I see that it breaks migration.
> 
> The fix is very simple, so I think it's OK for 4.2.. Still, it's not a
> degradation, so we may postpone it to 5.0.
> 
> Vladimir Sementsov-Ogievskiy (2):
>   block/qcow2-bitmap: fix bitmap migration
>   iotests: add new test cases to bitmap migration
> 
>  block/qcow2-bitmap.c       | 21 ++++++++++++++++++++-
>  tests/qemu-iotests/169     | 22 +++++++++++++++-------
>  tests/qemu-iotests/169.out |  4 ++--
>  3 files changed, 37 insertions(+), 10 deletions(-)

Thanks, applied to my block branch:

https://git.xanclic.moe/XanClic/qemu/commits/branch/block

Max


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