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authorJens Axboe <axboe@fb.com>2017-03-30 12:30:39 -0600
committerJens Axboe <axboe@fb.com>2017-03-30 12:30:39 -0600
commitbf4907c05e615f6a1811d61c58d56da52f7e9954 (patch)
treee63fd10fd38137403a56861e03bff6f1677d1ba7
parent47d752076a92c67f548faa018efd7d4ac51f17f7 (diff)
blk-mq: fix schedule-under-preempt for blocking drivers
Commit a4d907b6a33b unified the single and multi queue request handlers, but in the process, it also screwed up the locking balance and calls blk_mq_try_issue_directly() with the ctx preempt lock held. This is a problem for drivers that have set BLK_MQ_F_BLOCKING, since now they can't reliably sleep. While in there, protect against similar issues in the future, by adding a might_sleep() trigger in the BLOCKING path for direct issue or queue run. Reported-by: Josef Bacik <josef@toxicpanda.com> Tested-by: Josef Bacik <josef@toxicpanda.com> Fixes: a4d907b6a33b ("blk-mq: streamline blk_mq_make_request") Reviewed-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Jens Axboe <axboe@fb.com>
-rw-r--r--block/blk-mq.c17
1 files changed, 14 insertions, 3 deletions
diff --git a/block/blk-mq.c b/block/blk-mq.c
index ef63367077ad..061fc2cc88d3 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1121,6 +1121,8 @@ static void __blk_mq_run_hw_queue(struct blk_mq_hw_ctx *hctx)
blk_mq_sched_dispatch_requests(hctx);
rcu_read_unlock();
} else {
+ might_sleep();
+
srcu_idx = srcu_read_lock(&hctx->queue_rq_srcu);
blk_mq_sched_dispatch_requests(hctx);
srcu_read_unlock(&hctx->queue_rq_srcu, srcu_idx);
@@ -1495,7 +1497,11 @@ static void blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx,
__blk_mq_try_issue_directly(rq, cookie, false);
rcu_read_unlock();
} else {
- unsigned int srcu_idx = srcu_read_lock(&hctx->queue_rq_srcu);
+ unsigned int srcu_idx;
+
+ might_sleep();
+
+ srcu_idx = srcu_read_lock(&hctx->queue_rq_srcu);
__blk_mq_try_issue_directly(rq, cookie, true);
srcu_read_unlock(&hctx->queue_rq_srcu, srcu_idx);
}
@@ -1595,18 +1601,23 @@ static blk_qc_t blk_mq_make_request(struct request_queue *q, struct bio *bio)
list_del_init(&same_queue_rq->queuelist);
list_add_tail(&rq->queuelist, &plug->mq_list);
+ blk_mq_put_ctx(data.ctx);
+
if (same_queue_rq)
blk_mq_try_issue_directly(data.hctx, same_queue_rq,
&cookie);
+
+ return cookie;
} else if (q->nr_hw_queues > 1 && is_sync) {
+ blk_mq_put_ctx(data.ctx);
blk_mq_bio_to_request(rq, bio);
blk_mq_try_issue_directly(data.hctx, rq, &cookie);
+ return cookie;
} else if (q->elevator) {
blk_mq_bio_to_request(rq, bio);
blk_mq_sched_insert_request(rq, false, true, true, true);
- } else if (!blk_mq_merge_queue_io(data.hctx, data.ctx, rq, bio)) {
+ } else if (!blk_mq_merge_queue_io(data.hctx, data.ctx, rq, bio))
blk_mq_run_hw_queue(data.hctx, true);
- }
blk_mq_put_ctx(data.ctx);
return cookie;