effd60c878
monitor_qmp_dispatcher_co() runs in the iohandler AioContext that is not
polled during nested event loops. The coroutine currently reschedules
itself in the main loop's qemu_aio_context AioContext, which is polled
during nested event loops. One known problem is that QMP device-add
calls drain_call_rcu(), which temporarily drops the BQL, leading to all
sorts of havoc like other vCPU threads re-entering device emulation code
while another vCPU thread is waiting in device emulation code with
aio_poll().
Paolo Bonzini suggested running non-coroutine QMP handlers in the
iohandler AioContext. This avoids trouble with nested event loops. His
original idea was to move coroutine rescheduling to
monitor_qmp_dispatch(), but I resorted to moving it to qmp_dispatch()
because we don't know if the QMP handler needs to run in coroutine
context in monitor_qmp_dispatch(). monitor_qmp_dispatch() would have
been nicer since it's associated with the monitor implementation and not
as general as qmp_dispatch(), which is also used by qemu-ga.
A number of qemu-iotests need updated .out files because the order of
QMP events vs QMP responses has changed.
Solves Issue #1933.
Cc: qemu-stable@nongnu.org
Fixes: 7bed89958b ("device_core: use drain_call_rcu in in qmp_device_add")
Buglink: https://bugzilla.redhat.com/show_bug.cgi?id=2215192
Buglink: https://bugzilla.redhat.com/show_bug.cgi?id=2214985
Buglink: https://issues.redhat.com/browse/RHEL-17369
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-ID: <20240118144823.1497953-4-stefanha@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Tested-by: Fiona Ebner <f.ebner@proxmox.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
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25 lines
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QA output created by 140
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Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=65536
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wrote 65536/65536 bytes at offset 0
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64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
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{ 'execute': 'qmp_capabilities' }
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{"return": {}}
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{ 'execute': 'nbd-server-start',
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'arguments': { 'addr': { 'type': 'unix',
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'data': { 'path': 'SOCK_DIR/nbd' }}}}
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{"return": {}}
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{ 'execute': 'nbd-server-add',
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'arguments': { 'device': 'drv' }}
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{"return": {}}
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read 65536/65536 bytes at offset 0
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64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
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{ 'execute': 'eject',
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'arguments': { 'device': 'drv' }}
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{"timestamp": {"seconds": TIMESTAMP, "microseconds": TIMESTAMP}, "event": "BLOCK_EXPORT_DELETED", "data": {"id": "drv"}}
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qemu-io: can't open device nbd+unix:///drv?socket=SOCK_DIR/nbd: Requested export not available
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server reported: export 'drv' not present
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{ 'execute': 'quit' }
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{"timestamp": {"seconds": TIMESTAMP, "microseconds": TIMESTAMP}, "event": "SHUTDOWN", "data": {"guest": false, "reason": "host-qmp-quit"}}
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{"return": {}}
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*** done
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