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authorBart Van Assche <bart.vanassche@sandisk.com>2016-10-28 17:20:32 -0700
committerJens Axboe <axboe@fb.com>2016-11-02 12:50:19 -0600
commit52d7f1b5c2f33b5d34dc2b6af5175fb6a44999f6 (patch)
tree49b8487a5bece87f7cbcca4f77e4c9ec9dcb8e30 /drivers/scsi
parent2253efc850c4cf690516bbc07854eeb1077202ba (diff)
downloadlinux-52d7f1b5c2f33b5d34dc2b6af5175fb6a44999f6.tar.bz2
blk-mq: Avoid that requeueing starts stopped queues
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 <bart.vanassche@sandisk.com> Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> Cc: Roger Pau Monné <roger.pau@citrix.com> Cc: Mike Snitzer <snitzer@redhat.com> Cc: James Bottomley <jejb@linux.vnet.ibm.com> Cc: Martin K. Petersen <martin.petersen@oracle.com> Reviewed-by: Sagi Grimberg <sagi@grimberg.me> Reviewed-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Jens Axboe <axboe@fb.com>
Diffstat (limited to 'drivers/scsi')
-rw-r--r--drivers/scsi/scsi_lib.c1
1 files changed, 0 insertions, 1 deletions
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);