From 52d7f1b5c2f33b5d34dc2b6af5175fb6a44999f6 Mon Sep 17 00:00:00 2001 From: Bart Van Assche Date: Fri, 28 Oct 2016 17:20:32 -0700 Subject: [PATCH] blk-mq: Avoid that requeueing starts stopped queues MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Since blk_mq_requeue_work() starts stopped queues and since execution of this function can be scheduled after a queue has been stopped it is not possible to stop queues without using an additional state variable to track whether or not the queue has been stopped. Hence modify blk_mq_requeue_work() such that it does not start stopped queues. My conclusion after a review of the blk_mq_stop_hw_queues() and blk_mq_{delay_,}kick_requeue_list() callers is as follows: * In the dm driver starting and stopping queues should only happen if __dm_suspend() or __dm_resume() is called and not if the requeue list is processed. * In the SCSI core queue stopping and starting should only be performed by the scsi_internal_device_block() and scsi_internal_device_unblock() functions but not by any other function. Although the blk_mq_stop_hw_queue() call in scsi_queue_rq() may help to reduce CPU load if a LLD queue is full, figuring out whether or not a queue should be restarted when requeueing a command would require to introduce additional locking in scsi_mq_requeue_cmd() to avoid a race with scsi_internal_device_block(). Avoid this complexity by removing the blk_mq_stop_hw_queue() call from scsi_queue_rq(). * In the NVMe core only the functions that call blk_mq_start_stopped_hw_queues() explicitly should start stopped queues. * A blk_mq_start_stopped_hwqueues() call must be added in the xen-blkfront driver in its blkif_recover() function. Signed-off-by: Bart Van Assche Cc: Konrad Rzeszutek Wilk Cc: Roger Pau Monné Cc: Mike Snitzer Cc: James Bottomley Cc: Martin K. Petersen Reviewed-by: Sagi Grimberg Reviewed-by: Christoph Hellwig Signed-off-by: Jens Axboe --- block/blk-mq.c | 6 +----- drivers/block/xen-blkfront.c | 1 + drivers/md/dm-rq.c | 7 +------ drivers/scsi/scsi_lib.c | 1 - 4 files changed, 3 insertions(+), 12 deletions(-) diff --git a/block/blk-mq.c b/block/blk-mq.c index 447c37f39e32..d95034ae64f6 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -501,11 +501,7 @@ static void blk_mq_requeue_work(struct work_struct *work) blk_mq_insert_request(rq, false, false, false); } - /* - * Use the start variant of queue running here, so that running - * the requeue work will kick stopped queues. - */ - blk_mq_start_hw_queues(q); + blk_mq_run_hw_queues(q, false); } void blk_mq_add_to_requeue_list(struct request *rq, bool at_head) diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c index 9908597c5209..71ca36eab558 100644 --- a/drivers/block/xen-blkfront.c +++ b/drivers/block/xen-blkfront.c @@ -2045,6 +2045,7 @@ static int blkif_recover(struct blkfront_info *info) BUG_ON(req->nr_phys_segments > segs); blk_mq_requeue_request(req); } + blk_mq_start_stopped_hw_queues(info->rq, true); blk_mq_kick_requeue_list(info->rq); while ((bio = bio_list_pop(&info->bio_list)) != NULL) { diff --git a/drivers/md/dm-rq.c b/drivers/md/dm-rq.c index f76cc36b8546..a9e9e781bb77 100644 --- a/drivers/md/dm-rq.c +++ b/drivers/md/dm-rq.c @@ -338,12 +338,7 @@ static void dm_old_requeue_request(struct request *rq) static void __dm_mq_kick_requeue_list(struct request_queue *q, unsigned long msecs) { - unsigned long flags; - - spin_lock_irqsave(q->queue_lock, flags); - if (!blk_queue_stopped(q)) - blk_mq_delay_kick_requeue_list(q, msecs); - spin_unlock_irqrestore(q->queue_lock, flags); + blk_mq_delay_kick_requeue_list(q, msecs); } void dm_mq_kick_requeue_list(struct mapped_device *md) diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c index 8c52622ac257..2b78ff12bf3c 100644 --- a/drivers/scsi/scsi_lib.c +++ b/drivers/scsi/scsi_lib.c @@ -1952,7 +1952,6 @@ out_put_device: out: switch (ret) { case BLK_MQ_RQ_QUEUE_BUSY: - blk_mq_stop_hw_queue(hctx); if (atomic_read(&sdev->device_busy) == 0 && !scsi_device_blocked(sdev)) blk_mq_delay_queue(hctx, SCSI_QUEUE_DELAY);