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Re: [PATCH v4 4/4] iotests: Test node/bitmap aliases during migration


From: Vladimir Sementsov-Ogievskiy
Subject: Re: [PATCH v4 4/4] iotests: Test node/bitmap aliases during migration
Date: Thu, 20 Aug 2020 16:52:05 +0300
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.11.0

20.08.2020 16:17, Max Reitz wrote:
On 20.08.20 03:58, Eric Blake wrote:
On 8/18/20 8:32 AM, Max Reitz wrote:
Signed-off-by: Max Reitz <mreitz@redhat.com>
---
   tests/qemu-iotests/300     | 595 +++++++++++++++++++++++++++++++++++++
   tests/qemu-iotests/300.out |   5 +

Rather sparse output (I hate debugging those sorts of outputs when the
test is failing).

Hm.  I don’t know, the stack trace usually gives a good idea and
./check -d gives QMP context.

The advantage of a sparse output is that we don’t need to adjust the
reference output every time some optional field is added somewhere.

   tests/qemu-iotests/group   |   1 +
   3 files changed, 601 insertions(+)
   create mode 100755 tests/qemu-iotests/300
   create mode 100644 tests/qemu-iotests/300.out


+        # Dirty some random megabytes
+        for _ in range(9):
+            mb_ofs = random.randrange(1024)
+            self.vm_a.hmp_qemu_io(self.src_node_name, f'write
{mb_ofs}M 1M')

It turns out that the discard operation likewise dirties the bitmap, but
slightly faster (see edb90bbd).  We could optimize it on top, but I'm
not going to require a micro-optimizing to get it in.  The test takes
about 12 seconds to run for me, but you didn't mark it as such in
'group', so that's good; but it turns up a problem:

300      fail       [20:55:54] [20:56:06]                    output
mismatch (see 300.out.bad)
--- /home/eblake/qemu-tmp2/tests/qemu-iotests/300.out    2020-08-19
20:53:11.087791988 -0500
+++ /home/eblake/qemu-tmp2/tests/qemu-iotests/300.out.bad    2020-08-19
20:56:06.092428756 -0500
@@ -1,5 +1,41 @@
-.....................................
+WARNING:qemu.machine:qemu received signal 11; command:
"/home/eblake/qemu-tmp2/tests/qemu-iotests/../../x86_64-softmmu/qemu-system-x86_64
-display none -vga none -chardev
socket,id=mon,path=/tmp/tmp.qT831UThme/qemu-b-798452-monitor.sock -mon
chardev=mon,mode=control -qtest
unix:path=/tmp/tmp.qT831UThme/qemu-b-798452-qtest.sock -accel qtest
-nodefaults -display none -accel qtest -blockdev
node-name=node0,driver=null-co -incoming unix:/tmp/tmp.qT831UThme/mig_sock"
+.............FE.......................
+======================================================================
+ERROR: test_migratee_bitmap_is_not_mapped_on_dst
(__main__.TestBlockBitmapMappingErrors)
+----------------------------------------------------------------------
+Traceback (most recent call last):
+  File
"/home/eblake/qemu-tmp2/tests/qemu-iotests/../../python/qemu/machine.py", line
435, in _do_shutdown
+    self._soft_shutdown(timeout, has_quit)
+  File
"/home/eblake/qemu-tmp2/tests/qemu-iotests/../../python/qemu/machine.py", line
415, in _soft_shutdown
+    self._qmp.cmd('quit')
+  File
"/home/eblake/qemu-tmp2/tests/qemu-iotests/../../python/qemu/qmp.py",
line 266, in cmd
+    return self.cmd_obj(qmp_cmd)
+  File
"/home/eblake/qemu-tmp2/tests/qemu-iotests/../../python/qemu/qmp.py",
line 246, in cmd_obj
+    self.__sock.sendall(json.dumps(qmp_cmd).encode('utf-8'))
+BrokenPipeError: [Errno 32] Broken pipe
+
+The above exception was the direct cause of the following exception:
+
+Traceback (most recent call last):
+  File "300", line 76, in tearDown
+    self.vm_b.shutdown()
+  File
"/home/eblake/qemu-tmp2/tests/qemu-iotests/../../python/qemu/machine.py", line
465, in shutdown
+    self._do_shutdown(timeout, has_quit)
+  File
"/home/eblake/qemu-tmp2/tests/qemu-iotests/../../python/qemu/machine.py", line
438, in _do_shutdown
+    raise AbnormalShutdown("Could not perform graceful shutdown") \
+qemu.machine.AbnormalShutdown: Could not perform graceful shutdown
+
+======================================================================
+FAIL: test_migratee_bitmap_is_not_mapped_on_dst
(__main__.TestBlockBitmapMappingErrors)
+----------------------------------------------------------------------
+Traceback (most recent call last):
+  File "300", line 384, in test_migratee_bitmap_is_not_mapped_on_dst
+    self.migrate(False)
+  File "300", line 99, in migrate
+    self.assertEqual(self.vm_a.wait_migration('postmigrate'),
+AssertionError: False != True
+
  ----------------------------------------------------------------------
  Ran 37 tests

-OK
+FAILED (failures=1, errors=1)

I'm not sure why I'm seeing that, but it looks like you've got a bad
deref somewhere in the alias code.

Ah, crap.

This should fix it:

diff --git a/migration/block-dirty-bitmap.c b/migration/block-dirty-bitmap.c
index 89cb16b12c..d407dfefea 100644
--- a/migration/block-dirty-bitmap.c
+++ b/migration/block-dirty-bitmap.c
@@ -1091,7 +1091,9 @@ static int dirty_bitmap_load_header(QEMUFile *f,
DBMLoadState *s,
              } else {
                  bitmap_name = s->bitmap_alias;
              }
+        }

+        if (!s->cancelled) {
              g_strlcpy(s->bitmap_name, bitmap_name, sizeof(s->bitmap_name));
              s->bitmap = bdrv_find_dirty_bitmap(s->bs, s->bitmap_name);



That's correct thing to do

I had this originally, and then I decided to drop that hunk just before
sending v4 because I couldn’t see the point.  But we need it, because if
the bitmap alias is unknown, the migration is cancelled, so we need to
re-check s->cancalled after the alias lookup block.

Would you be OK with squashing that into patch 1?


Ok for me.

--
Best regards,
Vladimir



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