Commit
dce8921b2baaf95974af8176406881872067adfa ("iothread: Stop threads
before main() quits") introduced iothread_stop_all() to avoid the
following virtio-scsi assertion failure:
assert(blk_get_aio_context(d->conf.blk) == s->ctx);
Back then the assertion failed because when bdrv_close_all() made
d->conf.blk NULL, blk_get_aio_context() returned the global AioContext
instead of s->ctx.
The same assertion can still fail today when vcpus submit new I/O
requests after iothread_stop_all() has moved the BDS to the global
AioContext.
This patch hardens the iothread_stop_all() approach by pausing vcpus
before calling iothread_stop_all().
Note that the assertion failure is a race condition. It is not possible
to reproduce it reliably.
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-id:
20180201110708.8080-1-stefanha@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
main_loop();
replay_disable_events();
- iothread_stop_all();
+ /* The ordering of the following is delicate. Stop vcpus to prevent new
+ * I/O requests being queued by the guest. Then stop IOThreads (this
+ * includes a drain operation and completes all request processing). At
+ * this point emulated devices are still associated with their IOThreads
+ * (if any) but no longer have any work to do. Only then can we close
+ * block devices safely because we know there is no more I/O coming.
+ */
pause_all_vcpus();
+ iothread_stop_all();
bdrv_close_all();
+
res_free();
/* vhost-user must be cleaned up before chardevs. */