From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:34984 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1729855AbgBMMiM (ORCPT ); Thu, 13 Feb 2020 07:38:12 -0500 Received: from pps.filterd (m0098421.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.42/8.16.0.42) with SMTP id 01DCZFRm020696 for ; Thu, 13 Feb 2020 07:38:12 -0500 Received: from e06smtp05.uk.ibm.com (e06smtp05.uk.ibm.com [195.75.94.101]) by mx0a-001b2d01.pphosted.com with ESMTP id 2y4j8bkvw0-1 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NOT) for ; Thu, 13 Feb 2020 07:38:11 -0500 Received: from localhost by e06smtp05.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Thu, 13 Feb 2020 12:38:09 -0000 From: Halil Pasic Subject: [PATCH 1/2] virtio-blk: fix hw_queue stopped on arbitrary error Date: Thu, 13 Feb 2020 13:37:27 +0100 In-Reply-To: <20200213123728.61216-1-pasic@linux.ibm.com> References: <20200213123728.61216-1-pasic@linux.ibm.com> Message-Id: <20200213123728.61216-2-pasic@linux.ibm.com> Sender: linux-s390-owner@vger.kernel.org List-ID: To: "Michael S. Tsirkin" , Jason Wang Cc: Halil Pasic , Jens Axboe , Paolo Bonzini , Stefan Hajnoczi , virtualization@lists.linux-foundation.org, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org, Christian Borntraeger , Viktor Mihajlovski , Cornelia Huck , Ram Pai , Thiago Jung Bauermann , "Lendacky, Thomas" 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 Cc: Jens Axboe Fixes: f7728002c1c7 ("virtio_ring: fix return code on DMA mapping fails") --- I'm in doubt with regards to the Fixes tag. The thing is, virtio-blk probably made an assumption on virtqueue_add: the failure is either because the virtqueue is full, or the failure is fatal. In both cases it seems acceptable to stop the queue, although the fatal case is arguable. Since commit f7728002c1c7 it the dma mapping has failed returns -ENOMEM and not -EIO, and thus we have a recoverable failure that ain't virtqueue full. So I lean towards to a fixes tag that references that commit, although it ain't broken. Alternatively one could say 'Fixes: e467cde23818 ("Block driver using virtio.")', if the aforementioned assumption shouldn't have made in the first place. --- drivers/block/virtio_blk.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c index 54158766334b..adfe43f5ffe4 100644 --- a/drivers/block/virtio_blk.c +++ b/drivers/block/virtio_blk.c @@ -245,10 +245,12 @@ static blk_status_t virtio_queue_rq(struct blk_mq_hw_ctx *hctx, 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_STS_DEV_RESOURCE; return BLK_STS_IOERR; -- 2.17.1