vl.c/exit: pause cpus before closing block devices

There's a rare exit seg if the guest is accessing
IO during exit.
It's always hitting the atomic_inc(&bs->in_flight) with a NULL
bs. This was added recently in 99723548  but I don't see it
as the cause.

Flip vl.c around so we pause the cpus before closing the block devices,
that way we shouldn't have anything trying to access them when
they're gone.

This was originally Red Hat bz https://bugzilla.redhat.com/show_bug.cgi?id=1451015

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Reported-by: Cong Li <coli@redhat.com>
--
This is a very rare race, I'll leave it running in a loop to see if
we hit anything else and to check this really fixes it.

I do worry if there are other cases that can trigger this - e.g.
hot-unplug or ejecting a CD.

Message-Id: <20170713190116.21608-1-dgilbert@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
(cherry picked from commit 452589b6b47e8dc6353df257fc803dfc1383bed8)
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>

diff --git a/vl.c b/vl.c
index 0b4ed5241c8412c0533d2ffc134bcc4d26ad9072..c465eb2af2efbbb279f81f854bd4abda6a35c197 100644 (file)
--- a/vl.c
+++ b/vl.c
@@ -4710,8 +4710,8 @@ int main(int argc, char **argv, char **envp)
     replay_disable_events();
     iothread_stop_all();
 
-    bdrv_close_all();
     pause_all_vcpus();
+    bdrv_close_all();
     res_free();
 
     /* vhost-user must be cleaned up before chardevs.  */