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blk-mq: fix potential race in queue restart and driver tag allocation 

Once we mark the queue as needing a restart, re-check if we can
get a driver tag. This fixes a theoretical issue where the needed
IO completes _after_ blk_mq_get_driver_tag() fails, but before we
manage to set the restart bit.

Signed-off-by: Jens Axboe <axboe@fb.com>
Reviewed-by: Omar Sandoval <osandov@fb.com>
Tested-by: Hannes Reinecke <hare@suse.com>
This commit is contained in:
Jens Axboe 2017-01-26 12:50:36 -07:00
parent 0abad77412
commit 3c782d67c1
1 changed files with 9 additions and 1 deletions
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8
block/blk-mq.c
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@ -928,7 +928,15 @@ bool blk_mq_dispatch_rq_list(struct blk_mq_hw_ctx *hctx, struct list_head *list)
if (!blk_mq_get_driver_tag(rq, &hctx, false)) {
if (!queued && reorder_tags_to_front(list))
continue;
/*
* We failed getting a driver tag. Mark the queue(s)
* as needing a restart. Retry getting a tag again,
* in case the needed IO completed right before we
* marked the queue as needing a restart.
*/
blk_mq_sched_mark_restart(hctx);
if (!blk_mq_get_driver_tag(rq, &hctx, false))
break;
}
list_del_init(&rq->queuelist);