From: Halil Pasic pasic@linux.ibm.com
commit f5f6b95c72f7f8bb46eace8c5306c752d0133daa upstream.
Since nobody else is going to restart our hw_queue for us, the blk_mq_start_stopped_hw_queues() is in virtblk_done() is not sufficient necessarily sufficient to ensure that the queue will get started again. In case of global resource outage (-ENOMEM because mapping failure, because of swiotlb full) our virtqueue may be empty and we can get stuck with a stopped hw_queue.
Let us not stop the queue on arbitrary errors, but only on -EONSPC which indicates a full virtqueue, where the hw_queue is guaranteed to get started by virtblk_done() before when it makes sense to carry on submitting requests. Let us also remove a stale comment.
Signed-off-by: Halil Pasic pasic@linux.ibm.com Cc: Jens Axboe axboe@kernel.dk Fixes: f7728002c1c7 ("virtio_ring: fix return code on DMA mapping fails") Link: https://lore.kernel.org/r/20200213123728.61216-2-pasic@linux.ibm.com Signed-off-by: Michael S. Tsirkin mst@redhat.com Reviewed-by: Stefan Hajnoczi stefanha@redhat.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- drivers/block/virtio_blk.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-)
--- a/drivers/block/virtio_blk.c +++ b/drivers/block/virtio_blk.c @@ -215,10 +215,12 @@ static int virtio_queue_rq(struct blk_mq err = __virtblk_add_req(vblk->vqs[qid].vq, vbr, vbr->sg, num); if (err) { virtqueue_kick(vblk->vqs[qid].vq); - blk_mq_stop_hw_queue(hctx); + /* Don't stop the queue if -ENOMEM: we may have failed to + * bounce the buffer due to global resource outage. + */ + if (err == -ENOSPC) + blk_mq_stop_hw_queue(hctx); spin_unlock_irqrestore(&vblk->vqs[qid].lock, flags); - /* Out of mem doesn't actually happen, since we fall back - * to direct descriptors */ if (err == -ENOMEM || err == -ENOSPC) return BLK_MQ_RQ_QUEUE_BUSY; return BLK_MQ_RQ_QUEUE_ERROR;