Commit 184b9623 authored by Stefan Hajnoczi's avatar Stefan Hajnoczi
Browse files

virtio-scsi: fix race between .ioeventfd_stop() and vq handler 



If the main loop thread invokes .ioeventfd_stop() just as the vq handler
function begins in the IOThread then the handler may lose the race for
the AioContext lock.  By the time the vq handler is able to acquire the
AioContext lock the ioeventfd has already been removed and the handler
isn't supposed to run anymore!

Use the new aio_wait_bh_oneshot() function to perform ioeventfd removal
from within the IOThread.  This way no races with the vq handler are
possible.

Signed-off-by: default avatarStefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: default avatarFam Zheng <famz@redhat.com>
Acked-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
Message-id: 20180307144205.20619-4-stefanha@redhat.com
Signed-off-by: default avatarStefan Hajnoczi <stefanha@redhat.com>
parent 1010cadf

hw/scsi/virtio-scsi-dataplane.c

+5 −4
Original line number Diff line number Diff line
@@ -107,9 +107,10 @@ static int virtio_scsi_vring_init(VirtIOSCSI *s, VirtQueue *vq, int n, 
    return 0;

}



/* assumes s->ctx held */

static void virtio_scsi_clear_aio(VirtIOSCSI *s)

/* Context: BH in IOThread */

static void virtio_scsi_dataplane_stop_bh(void *opaque)

{

    VirtIOSCSI *s = opaque;

    VirtIOSCSICommon *vs = VIRTIO_SCSI_COMMON(s);

    int i;
@@ -171,7 +172,7 @@ int virtio_scsi_dataplane_start(VirtIODevice *vdev) 
    return 0;



fail_vrings:

    virtio_scsi_clear_aio(s);

    aio_wait_bh_oneshot(s->ctx, virtio_scsi_dataplane_stop_bh, s);

    aio_context_release(s->ctx);

    for (i = 0; i < vs->conf.num_queues + 2; i++) {

        virtio_bus_set_host_notifier(VIRTIO_BUS(qbus), i, false);
@@ -207,7 +208,7 @@ void virtio_scsi_dataplane_stop(VirtIODevice *vdev) 
    s->dataplane_stopping = true;



    aio_context_acquire(s->ctx);

    virtio_scsi_clear_aio(s);

    aio_wait_bh_oneshot(s->ctx, virtio_scsi_dataplane_stop_bh, s);

    aio_context_release(s->ctx);



    blk_drain_all(); /* ensure there are no in-flight requests */