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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Christoph Hellwig <hch@lst.de>,
        Hannes Reinecke <hare@suse.de>,
        David Milburn <dmilburn@redhat.com>,
        "Ewan D. Milne" <emilne@redhat.com>,
        Ming Lei <ming.lei@redhat.com>, Jens Axboe <axboe@kernel.dk>,
        Sasha Levin <sashal@kernel.org>
Subject: [PATCH 5.9 662/757] blk-mq: always allow reserved allocation in hctx_may_queue
Date:   Tue, 27 Oct 2020 14:55:12 +0100
Message-Id: <20201027135521.592311582@linuxfoundation.org>
In-Reply-To: <20201027135450.497324313@linuxfoundation.org>
References: <20201027135450.497324313@linuxfoundation.org>
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From: Ming Lei <ming.lei@redhat.com>

[ Upstream commit 285008501c65a3fcee05d2c2c26cbf629ceff2f0 ]

NVMe shares tagset between fabric queue and admin queue or between
connect_q and NS queue, so hctx_may_queue() can be called to allocate
request for these queues.

Tags can be reserved in these tagset. Before error recovery, there is
often lots of in-flight requests which can't be completed, and new
reserved request may be needed in error recovery path. However,
hctx_may_queue() can always return false because there is too many
in-flight requests which can't be completed during error handling.
Finally, nothing can proceed.

Fix this issue by always allowing reserved tag allocation in
hctx_may_queue(). This is reasonable because reserved tags are supposed
to always be available.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Cc: David Milburn <dmilburn@redhat.com>
Cc: Ewan D. Milne <emilne@redhat.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 block/blk-mq-tag.c | 3 ++-
 block/blk-mq.c     | 5 +++--
 2 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c
index 32d82e23b0953..a1c1e7c611f7b 100644
--- a/block/blk-mq-tag.c
+++ b/block/blk-mq-tag.c
@@ -59,7 +59,8 @@ void __blk_mq_tag_idle(struct blk_mq_hw_ctx *hctx)
 static int __blk_mq_get_tag(struct blk_mq_alloc_data *data,
 			    struct sbitmap_queue *bt)
 {
-	if (!data->q->elevator && !hctx_may_queue(data->hctx, bt))
+	if (!data->q->elevator && !(data->flags & BLK_MQ_REQ_RESERVED) &&
+			!hctx_may_queue(data->hctx, bt))
 		return BLK_MQ_NO_TAG;
 
 	if (data->shallow_depth)
diff --git a/block/blk-mq.c b/block/blk-mq.c
index c27a61029cdd0..94a53d779c12b 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1105,10 +1105,11 @@ static bool __blk_mq_get_driver_tag(struct request *rq)
 	if (blk_mq_tag_is_reserved(rq->mq_hctx->sched_tags, rq->internal_tag)) {
 		bt = &rq->mq_hctx->tags->breserved_tags;
 		tag_offset = 0;
+	} else {
+		if (!hctx_may_queue(rq->mq_hctx, bt))
+			return false;
 	}
 
-	if (!hctx_may_queue(rq->mq_hctx, bt))
-		return false;
 	tag = __sbitmap_queue_get(bt);
 	if (tag == BLK_MQ_NO_TAG)
 		return false;
-- 
2.25.1