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| author | Stefan Hajnoczi | 2017-05-08 20:07:05 +0200 |
|---|---|---|
| committer | Stefan Hajnoczi | 2017-05-12 16:36:46 +0200 |
| commit | 321d1dba8bef9676a77e9399484e3cd8bf2cf16a (patch) | |
| tree | 6d704c21e6afff48cd7bd7bb68b50b80b641dcc7 /include/block | |
| parent | block: Simplify BDRV_BLOCK_RAW recursion (diff) | |
| download | qemu-321d1dba8bef9676a77e9399484e3cd8bf2cf16a.tar.gz qemu-321d1dba8bef9676a77e9399484e3cd8bf2cf16a.tar.xz qemu-321d1dba8bef9676a77e9399484e3cd8bf2cf16a.zip | |
aio: add missing aio_notify() to aio_enable_external()
The main loop uses aio_disable_external()/aio_enable_external() to
temporarily disable processing of external AioContext clients like
device emulation.
This allows monitor commands to quiesce I/O and prevent the guest from
submitting new requests while a monitor command is in progress.
The aio_enable_external() API is currently broken when an IOThread is in
aio_poll() waiting for fd activity when the main loop re-enables
external clients. Incrementing ctx->external_disable_cnt does not wake
the IOThread from ppoll(2) so fd processing remains suspended and leads
to unresponsive emulated devices.
This patch adds an aio_notify() call to aio_enable_external() so the
IOThread is kicked out of ppoll(2) and will re-arm the file descriptors.
The bug can be reproduced as follows:
$ qemu -M accel=kvm -m 1024 \
-object iothread,id=iothread0 \
-device virtio-scsi-pci,iothread=iothread0,id=virtio-scsi-pci0 \
-drive if=none,id=drive0,aio=native,cache=none,format=raw,file=test.img \
-device scsi-hd,id=scsi-hd0,drive=drive0 \
-qmp tcp::5555,server,nowait
$ scripts/qmp/qmp-shell localhost:5555
(qemu) blockdev-snapshot-sync device=drive0 snapshot-file=sn1.qcow2
mode=absolute-paths format=qcow2
After blockdev-snapshot-sync completes the SCSI disk will be
unresponsive. This leads to request timeouts inside the guest.
Reported-by: Qianqian Zhu <qizhu@redhat.com>
Reviewed-by: Fam Zheng <famz@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-id: 20170508180705.20609-1-stefanha@redhat.com
Suggested-by: Fam Zheng <famz@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Diffstat (limited to 'include/block')
| -rw-r--r-- | include/block/aio.h | 10 |
1 files changed, 8 insertions, 2 deletions
diff --git a/include/block/aio.h b/include/block/aio.h index 406e32305a..e9aeeaec94 100644 --- a/include/block/aio.h +++ b/include/block/aio.h @@ -454,8 +454,14 @@ static inline void aio_disable_external(AioContext *ctx) */ static inline void aio_enable_external(AioContext *ctx) { - assert(ctx->external_disable_cnt > 0); - atomic_dec(&ctx->external_disable_cnt); + int old; + + old = atomic_fetch_dec(&ctx->external_disable_cnt); + assert(old > 0); + if (old == 1) { + /* Kick event loop so it re-arms file descriptors */ + aio_notify(ctx); + } } /** |