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bdrv_unref() is called by a lot of places that need to hold the graph lock (it naturally happens in the context of operations that change the graph). However, bdrv_unref() takes the graph writer lock internally, so it can't actually be called while already holding a graph lock without causing a deadlock. bdrv_unref() also can't just become GRAPH_WRLOCK because it drains the node before closing it, and draining requires that the graph is unlocked. The solution is to defer deleting the node until we don't hold the lock any more and draining is possible again. Note that keeping images open for longer than necessary can create problems, too: You can't open an image again before it is really closed (if image locking didn't prevent it, it would cause corruption). Reopening an image immediately happens at least during bdrv_open() and bdrv_co_create(). In order to solve this problem, make sure to run the deferred unref in bdrv_graph_wrunlock(), i.e. the first possible place where we can drain again. This is also why bdrv_schedule_unref() is marked GRAPH_WRLOCK. The output of iotest 051 is updated because the additional polling changes the order of HMP output, resulting in a new "(qemu)" prompt in the test output that was previously on a separate line and filtered out. Signed-off-by: Kevin Wolf <kwolf@redhat.com> Message-ID: <20230911094620.45040-6-kwolf@redhat.com> Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com> Signed-off-by: Kevin Wolf <kwolf@redhat.com> |
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| .. | ||
| accounting.h | ||
| aio-wait.h | ||
| aio.h | ||
| aio_task.h | ||
| block-common.h | ||
| block-copy.h | ||
| block-global-state.h | ||
| block-hmp-cmds.h | ||
| block-io.h | ||
| block.h | ||
| block_backup.h | ||
| block_int-common.h | ||
| block_int-global-state.h | ||
| block_int-io.h | ||
| block_int.h | ||
| blockjob.h | ||
| blockjob_int.h | ||
| dirty-bitmap.h | ||
| export.h | ||
| fuse.h | ||
| graph-lock.h | ||
| nbd.h | ||
| nvme.h | ||
| qapi.h | ||
| qdict.h | ||
| raw-aio.h | ||
| replication.h | ||
| reqlist.h | ||
| snapshot.h | ||
| thread-pool.h | ||
| throttle-groups.h | ||
| ufs.h | ||
| write-threshold.h | ||