Commit 0df21c86bdbf introduced several bugs:
* A SCSI queue stall for queue depths > 1, addressed by commit
88022d7201e9 ("blk-mq: don't handle failure in .get_budget")
* A systematic lockup for SCSI queues with queue depth 1. The
following test reproduces that bug systematically:
- Change the SRP initiator such that SCSI target queue depth is
limited to 1.
- Run the following command:
srp-test/run_tests -f xfs -d -e none -r 60 -t 01
See also "[PATCH 4/7] blk-mq: Avoid that request processing
stalls when sharing tags"
(https://marc.info/?l=linux-block&m=151208695316857). Note:
reverting commit 0df21c86bdbf also fixes a sporadic SCSI request
queue lockup while inserting a blk_mq_sched_mark_restart_hctx()
before all blk_mq_dispatch_rq_list() calls only fixes the
systematic lockup for queue depth 1.
* A scsi_debug lockup - see also "[PATCH] SCSI: delay run queue if
device is blocked in scsi_dev_queue_ready()"
(https://marc.info/?l=linux-block&m=151223233407154).
I think the above means that it is too risky to try to fix all bugs
introduced by commit 0df21c86bdbf before kernel v4.15 is released.
Hence revert that commit.
Fixes: commit 0df21c86bdbf ("scsi: implement .get_budget and .put_budget for blk-mq")
Signed-off-by: Bart Van Assche <bart.vanassche@xxxxxxx>
Cc: Ming Lei <ming.lei@xxxxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxx>
Cc: Hannes Reinecke <hare@xxxxxxxx>
Cc: Johannes Thumshirn <jthumshirn@xxxxxxx>
Cc: James E.J. Bottomley <jejb@xxxxxxxxxxxxxxxxxx>
Cc: Martin K. Petersen <martin.petersen@xxxxxxxxxx>
Cc: linux-scsi@xxxxxxxxxxxxxxx
---
drivers/scsi/scsi_lib.c | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)
diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index 84bd2b16d216..a7e7966f1477 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -1976,9 +1976,11 @@ static blk_status_t scsi_queue_rq(struct blk_mq_hw_ctx *hctx,
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;
+ blk_status_t ret = BLK_STS_RESOURCE;
int reason;
+ if (!scsi_mq_get_budget(hctx))
+ goto out;
ret = prep_to_mq(scsi_prep_state_check(sdev, req));
if (ret != BLK_STS_OK)
goto out_put_budget;
@@ -2022,6 +2024,7 @@ static blk_status_t scsi_queue_rq(struct blk_mq_hw_ctx *hctx,
atomic_dec(&scsi_target(sdev)->target_busy);
out_put_budget:
scsi_mq_put_budget(hctx);
+out:
switch (ret) {
case BLK_STS_OK:
break;
@@ -2225,8 +2228,6 @@ struct request_queue *scsi_old_alloc_queue(struct scsi_device *sdev)
}
static const struct blk_mq_ops scsi_mq_ops = {
- .get_budget = scsi_mq_get_budget,
- .put_budget = scsi_mq_put_budget,
.queue_rq = scsi_queue_rq,
.complete = scsi_softirq_done,
.timeout = scsi_timeout,
--
2.15.0
