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iotest 151: add test-case that shows active mirror dead-lock

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There is a dead-lock in active mirror: when we have parallel
intersecting requests (note that non intersecting requests may be
considered intersecting after aligning to mirror granularity), it may
happen that request A waits request B in mirror_wait_on_conflicts() and
request B waits for A.

Look at the test for details. Test now dead-locks, that's why it's
disabled. Next commit will fix mirror and enable the test.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Message-Id: <20210702211636.228981-3-vsementsov@virtuozzo.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Vladimir Sementsov-Ogievskiy 2021-07-03 00:16:35 +03:00 committed by Kevin Wolf
parent ead3f1bff9
commit e0f69d83d5
2 changed files with 62 additions and 4 deletions
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62
tests/qemu-iotests/151
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@ -38,8 +38,9 @@ class TestActiveMirror(iotests.QMPTestCase):
'if': 'none',
'node-name': 'source-node',
'driver': iotests.imgfmt,
'file': {'driver': 'file',
'filename': source_img}}
'file': {'driver': 'blkdebug',
'image': {'driver': 'file',
'filename': source_img}}}
blk_target = {'node-name': 'target-node',
'driver': iotests.imgfmt,
@ -141,6 +142,63 @@ class TestActiveMirror(iotests.QMPTestCase):
self.potential_writes_in_flight = False
def testIntersectingActiveIO(self):
# FIXME: test-case is dead-locking. To reproduce dead-lock just drop
# this return statement
return
# Fill the source image
result = self.vm.hmp_qemu_io('source', 'write -P 1 0 2M')
# Start the block job (very slowly)
result = self.vm.qmp('blockdev-mirror',
job_id='mirror',
filter_node_name='mirror-node',
device='source-node',
target='target-node',
sync='full',
copy_mode='write-blocking',
speed=1)
self.vm.hmp_qemu_io('source', 'break write_aio A')
self.vm.hmp_qemu_io('source', 'aio_write 0 1M') # 1
self.vm.hmp_qemu_io('source', 'wait_break A')
self.vm.hmp_qemu_io('source', 'aio_write 0 2M') # 2
self.vm.hmp_qemu_io('source', 'aio_write 0 2M') # 3
# Now 2 and 3 are in mirror_wait_on_conflicts, waiting for 1
self.vm.hmp_qemu_io('source', 'break write_aio B')
self.vm.hmp_qemu_io('source', 'aio_write 1M 2M') # 4
self.vm.hmp_qemu_io('source', 'wait_break B')
# 4 doesn't wait for 2 and 3, because they didn't yet set
# in_flight_bitmap. So, nothing prevents 4 to go except for our
# break-point B.
self.vm.hmp_qemu_io('source', 'resume A')
# Now we resumed 1, so 2 and 3 goes to the next iteration of while loop
# in mirror_wait_on_conflicts(). They don't exit, as bitmap is dirty
# due to request 4. And they start to wait: 2 wait for 3, 3 wait for 2
# - DEAD LOCK.
# Note that it's important that we add request 4 at last: requests are
# appended to the list, so we are sure that 4 is last in the list, so 2
# and 3 now waits for each other, not for 4.
self.vm.hmp_qemu_io('source', 'resume B')
# Resuming 4 doesn't help, 2 and 3 already dead-locked
# To check the dead-lock run:
# gdb -p $(pidof qemu-system-x86_64) -ex 'set $job=(MirrorBlockJob *)jobs.lh_first' -ex 'p *$job->ops_in_flight.tqh_first' -ex 'p *$job->ops_in_flight.tqh_first->next.tqe_next'
# You'll see two MirrorOp objects waiting on each other
result = self.vm.qmp('block-job-set-speed', device='mirror', speed=0)
self.assert_qmp(result, 'return', {})
self.complete_and_wait(drive='mirror')
self.potential_writes_in_flight = False
if __name__ == '__main__':
iotests.main(supported_fmts=['qcow2', 'raw'],

4
tests/qemu-iotests/151.out
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@ -1,5 +1,5 @@
...
....
----------------------------------------------------------------------
Ran 3 tests
Ran 4 tests
OK