From bf4907c05e615f6a1811d61c58d56da52f7e9954 Mon Sep 17 00:00:00 2001 From: Jens Axboe Date: Thu, 30 Mar 2017 12:30:39 -0600 Subject: [PATCH] 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 Tested-by: Josef Bacik Fixes: a4d907b6a33b ("blk-mq: streamline blk_mq_make_request") Reviewed-by: Christoph Hellwig Signed-off-by: Jens Axboe --- block/blk-mq.c | 17 ++++++++++++++--- 1 file 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; -- 2.20.1