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block/mirror: fix active mirror dead-lock in mirror_wait_on_conflicts
It's possible that requests start to wait each other in
mirror_wait_on_conflicts(). To avoid it let's use same technique as in
block/io.c in bdrv_wait_serialising_requests_locked() /
bdrv_find_conflicting_request(): don't wait on intersecting request if
it is already waiting for some other request.
For details of the dead-lock look at testIntersectingActiveIO()
test-case which we actually fixing now.
Fixes: d06107ade0
Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Message-Id: <20210702211636.228981-4-vsementsov@virtuozzo.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
parent
e0f69d83d5
commit
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@ -107,6 +107,7 @@ struct MirrorOp {
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bool is_in_flight;
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CoQueue waiting_requests;
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Coroutine *co;
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MirrorOp *waiting_for_op;
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QTAILQ_ENTRY(MirrorOp) next;
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};
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@ -159,7 +160,18 @@ static void coroutine_fn mirror_wait_on_conflicts(MirrorOp *self,
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if (ranges_overlap(self_start_chunk, self_nb_chunks,
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op_start_chunk, op_nb_chunks))
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{
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/*
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* If the operation is already (indirectly) waiting for us, or
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* will wait for us as soon as it wakes up, then just go on
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* (instead of producing a deadlock in the former case).
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*/
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if (op->waiting_for_op) {
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continue;
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}
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self->waiting_for_op = op;
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qemu_co_queue_wait(&op->waiting_requests, NULL);
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self->waiting_for_op = NULL;
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break;
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}
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}
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@ -143,10 +143,6 @@ class TestActiveMirror(iotests.QMPTestCase):
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self.potential_writes_in_flight = False
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def testIntersectingActiveIO(self):
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# FIXME: test-case is dead-locking. To reproduce dead-lock just drop
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# this return statement
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return
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# Fill the source image
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result = self.vm.hmp_qemu_io('source', 'write -P 1 0 2M')
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@ -180,18 +176,14 @@ class TestActiveMirror(iotests.QMPTestCase):
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# Now we resumed 1, so 2 and 3 goes to the next iteration of while loop
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# in mirror_wait_on_conflicts(). They don't exit, as bitmap is dirty
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# due to request 4. And they start to wait: 2 wait for 3, 3 wait for 2
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# - DEAD LOCK.
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# Note that it's important that we add request 4 at last: requests are
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# appended to the list, so we are sure that 4 is last in the list, so 2
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# and 3 now waits for each other, not for 4.
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# due to request 4.
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# In the past at that point 2 and 3 would wait for each other producing
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# a dead-lock. Now this is fixed and they will wait for request 4.
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self.vm.hmp_qemu_io('source', 'resume B')
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# Resuming 4 doesn't help, 2 and 3 already dead-locked
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# To check the dead-lock run:
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# 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'
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# You'll see two MirrorOp objects waiting on each other
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# After resuming 4, one of 2 and 3 goes first and set in_flight_bitmap,
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# so the other will wait for it.
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result = self.vm.qmp('block-job-set-speed', device='mirror', speed=0)
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self.assert_qmp(result, 'return', {})
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