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authorStefan Hajnoczi <stefanha@redhat.com>2017-05-08 14:07:05 -0400
committerStefan Hajnoczi <stefanha@redhat.com>2017-05-12 10:36:46 -0400
commit321d1dba8bef9676a77e9399484e3cd8bf2cf16a (patch)
tree6d704c21e6afff48cd7bd7bb68b50b80b641dcc7 /include
parentee29d6adefcca7e76abb124183814ed3acc74fac (diff)
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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')
-rw-r--r--include/block/aio.h10
1 files changed, 8 insertions, 2 deletions
diff --git a/include/block/aio.h b/include/block/aio.h
index 406e323..e9aeeae 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);
+ }
}
/**