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| author | Bart Van Assche <bart.vanassche@sandisk.com> | 2016-10-28 17:20:32 -0700 |
|---|---|---|
| committer | Jens Axboe <axboe@fb.com> | 2016-11-02 12:50:19 -0600 |
| commit | 52d7f1b5c2f33b5d34dc2b6af5175fb6a44999f6 (patch) | |
| tree | 49b8487a5bece87f7cbcca4f77e4c9ec9dcb8e30 /drivers/block | |
| parent | 2253efc850c4cf690516bbc07854eeb1077202ba (diff) | |
| download | linux-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/block')
| -rw-r--r-- | drivers/block/xen-blkfront.c | 1 |
1 files changed, 1 insertions, 0 deletions
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) { |