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monitor: only run coroutine commands in qemu_aio_context

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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>
This commit is contained in:
Stefan Hajnoczi 2024-01-18 09:48:23 -05:00 • committed by Kevin Wolf
parent 9ee2dd4c22
commit effd60c878
32 changed files with 207 additions and 180 deletions
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4
tests/qemu-iotests/109
View file

@ -57,13 +57,13 @@ run_qemu()
_launch_qemu -drive file="${source_img}",format=raw,cache=${CACHEMODE},aio=${AIOMODE},id=src
_send_qemu_cmd $QEMU_HANDLE "{ 'execute': 'qmp_capabilities' }" "return"
_send_qemu_cmd $QEMU_HANDLE \
capture_events="$qmp_event" _send_qemu_cmd $QEMU_HANDLE \
"{'execute':'drive-mirror', 'arguments':{
'device': 'src', 'target': '$raw_img', $qmp_format
'mode': 'existing', 'sync': 'full'}}" \
"return"
_send_qemu_cmd $QEMU_HANDLE '' "$qmp_event"
capture_events="$qmp_event JOB_STATUS_CHANGE" _wait_event $QEMU_HANDLE "$qmp_event"
if test "$qmp_event" = BLOCK_JOB_ERROR; then
_send_qemu_cmd $QEMU_HANDLE '' '"status": "null"'
fi