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authorStefan Hajnoczi <stefanha@redhat.com>2018-02-01 11:07:08 +0000
committerStefan Hajnoczi <stefanha@redhat.com>2018-02-15 09:39:49 +0000
commit00d09fdbbae5f7864ce754913efc84c12fdf9f1a (patch)
treef6085750008fb10a013c0a4917ac5198fafd3781 /vl.c
parentbec9c64ef7be8063f1192608b83877bc5c9ea217 (diff)
vl: pause vcpus before stopping iothreads
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>
Diffstat (limited to 'vl.c')
-rw-r--r--vl.c10
1 files changed, 9 insertions, 1 deletions
diff --git a/vl.c b/vl.c
index 21878496ec..7a5554bc41 100644
--- a/vl.c
+++ b/vl.c
@@ -4767,10 +4767,18 @@ int main(int argc, char **argv, char **envp)
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. */