From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx1.redhat.com ([209.132.183.28]:54620 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751419AbdKDBz5 (ORCPT ); Fri, 3 Nov 2017 21:55:57 -0400 From: Ming Lei To: Jens Axboe , linux-block@vger.kernel.org, Christoph Hellwig Cc: Bart Van Assche , Laurence Oberman , linux-scsi@vger.kernel.org, Omar Sandoval , John Garry , Ming Lei Subject: [PATCH] SCSI: don't get target/host busy_count in scsi_mq_get_budget() Date: Sat, 4 Nov 2017 09:55:34 +0800 Message-Id: <20171104015534.32684-1-ming.lei@redhat.com> Sender: linux-block-owner@vger.kernel.org List-Id: linux-block@vger.kernel.org It is very expensive to atomic_inc/atomic_dec the host wide counter of host->busy_count, and it should have been avoided via blk-mq's mechanism of getting driver tag, which uses the more efficient way of sbitmap queue. Also we don't check atomic_read(&sdev->device_busy) in scsi_mq_get_budget() and don't run queue if the counter becomes zero, so IO hang may be caused if all requests are completed just before the current SCSI device is added to shost->starved_list. Fixes: 0df21c86bdbf(scsi: implement .get_budget and .put_budget for blk-mq) Reported-by: Bart Van Assche Signed-off-by: Ming Lei --- drivers/scsi/scsi_lib.c | 29 +++++++++++++---------------- 1 file changed, 13 insertions(+), 16 deletions(-) diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c index a098af3070a1..7f218ef61900 100644 --- a/drivers/scsi/scsi_lib.c +++ b/drivers/scsi/scsi_lib.c @@ -1944,11 +1944,7 @@ static void scsi_mq_put_budget(struct blk_mq_hw_ctx *hctx) { struct request_queue *q = hctx->queue; struct scsi_device *sdev = q->queuedata; - struct Scsi_Host *shost = sdev->host; - atomic_dec(&shost->host_busy); - if (scsi_target(sdev)->can_queue > 0) - atomic_dec(&scsi_target(sdev)->target_busy); atomic_dec(&sdev->device_busy); put_device(&sdev->sdev_gendev); } @@ -1957,7 +1953,6 @@ static blk_status_t scsi_mq_get_budget(struct blk_mq_hw_ctx *hctx) { struct request_queue *q = hctx->queue; struct scsi_device *sdev = q->queuedata; - struct Scsi_Host *shost = sdev->host; blk_status_t ret; ret = prep_to_mq(scsi_prep_state_check(sdev, NULL)); @@ -1968,18 +1963,9 @@ static blk_status_t scsi_mq_get_budget(struct blk_mq_hw_ctx *hctx) goto out; if (!scsi_dev_queue_ready(q, sdev)) goto out_put_device; - if (!scsi_target_queue_ready(shost, sdev)) - goto out_dec_device_busy; - if (!scsi_host_queue_ready(q, shost, sdev)) - goto out_dec_target_busy; return BLK_STS_OK; -out_dec_target_busy: - if (scsi_target(sdev)->can_queue > 0) - atomic_dec(&scsi_target(sdev)->target_busy); -out_dec_device_busy: - atomic_dec(&sdev->device_busy); out_put_device: put_device(&sdev->sdev_gendev); out: @@ -1992,6 +1978,7 @@ static blk_status_t scsi_queue_rq(struct blk_mq_hw_ctx *hctx, struct request *req = bd->rq; struct request_queue *q = req->q; struct scsi_device *sdev = q->queuedata; + struct Scsi_Host *shost = sdev->host; struct scsi_cmnd *cmd = blk_mq_rq_to_pdu(req); blk_status_t ret; int reason; @@ -2001,10 +1988,15 @@ static blk_status_t scsi_queue_rq(struct blk_mq_hw_ctx *hctx, goto out_put_budget; ret = BLK_STS_RESOURCE; + if (!scsi_target_queue_ready(shost, sdev)) + goto out_put_budget; + if (!scsi_host_queue_ready(q, shost, sdev)) + goto out_dec_target_busy; + if (!(req->rq_flags & RQF_DONTPREP)) { ret = prep_to_mq(scsi_mq_prep_fn(req)); if (ret != BLK_STS_OK) - goto out_put_budget; + goto out_dec_host_busy; req->rq_flags |= RQF_DONTPREP; } else { blk_mq_start_request(req); @@ -2022,11 +2014,16 @@ static blk_status_t scsi_queue_rq(struct blk_mq_hw_ctx *hctx, if (reason) { scsi_set_blocked(cmd, reason); ret = BLK_STS_RESOURCE; - goto out_put_budget; + goto out_dec_host_busy; } return BLK_STS_OK; +out_dec_host_busy: + atomic_dec(&shost->host_busy); +out_dec_target_busy: + if (scsi_target(sdev)->can_queue > 0) + atomic_dec(&scsi_target(sdev)->target_busy); out_put_budget: scsi_mq_put_budget(hctx); switch (ret) { -- 2.9.5