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Thu, 12 Nov 2020 02:55:43 -0500 X-MC-Unique: YPELfsR9Nr6GGXG1ubt9Qw-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id ADCCA190A3E0; Thu, 12 Nov 2020 07:55:41 +0000 (UTC) Received: from localhost (ovpn-12-132.pek2.redhat.com [10.72.12.132]) by smtp.corp.redhat.com (Postfix) with ESMTP id ECB1F5C62B; Thu, 12 Nov 2020 07:55:40 +0000 (UTC) From: Ming Lei To: Jens Axboe , linux-block@vger.kernel.org, linux-nvme@lists.infradead.org, Christoph Hellwig Subject: [PATCH 1/3] blk-mq: add new API of blk_mq_hctx_set_fq_lock_class Date: Thu, 12 Nov 2020 15:55:24 +0800 Message-Id: <20201112075526.947079-2-ming.lei@redhat.com> In-Reply-To: <20201112075526.947079-1-ming.lei@redhat.com> References: <20201112075526.947079-1-ming.lei@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20201112_025547_643875_118EB5D3 X-CRM114-Status: GOOD ( 17.50 ) X-BeenThere: linux-nvme@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Bart Van Assche , Qian Cai , John Garry , Kashyap Desai , Sumit Saxena , Hannes Reinecke , Ming Lei Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "Linux-nvme" Errors-To: linux-nvme-bounces+linux-nvme=archiver.kernel.org@lists.infradead.org flush_end_io() may be called recursively from some driver, such as nvme-loop, so lockdep may complain 'possible recursive locking'. Commit b3c6a5997541("block: Fix a lockdep complaint triggered by request queue flushing") tried to address this issue by assigning dynamically allocated per-flush-queue lock class. This solution adds synchronize_rcu() for each hctx's release handler, and causes horrible SCSI MQ probe delay(more than half an hour on megaraid sas). Add new API of blk_mq_hctx_set_fq_lock_class() for these drivers, so we just need to use driver specific lock class for avoiding the lockdep warning of 'possible recursive locking'. Reported-by: Qian Cai Cc: Sumit Saxena Cc: John Garry Cc: Kashyap Desai Cc: Bart Van Assche Cc: Hannes Reinecke Signed-off-by: Ming Lei --- block/blk-flush.c | 25 +++++++++++++++++++++++++ include/linux/blk-mq.h | 3 +++ 2 files changed, 28 insertions(+) diff --git a/block/blk-flush.c b/block/blk-flush.c index e32958f0b687..657743524e15 100644 --- a/block/blk-flush.c +++ b/block/blk-flush.c @@ -490,3 +490,28 @@ void blk_free_flush_queue(struct blk_flush_queue *fq) kfree(fq->flush_rq); kfree(fq); } + +/* + * Allow driver to set its own lock class to fq->mq_flush_lock for + * avoiding lockdep complaint. + * + * flush_end_io() may be called recursively from some driver, such as + * nvme-loop, so lockdep may complain 'possible recursive locking' because + * all 'struct blk_flush_queue' instance share same mq_flush_lock lock class + * key. We need to assign different lock class for these driver's + * fq->mq_flush_lock for avoiding the lockdep warning. + * + * Use dynamically allocated lock class key for each 'blk_flush_queue' + * instance is over-kill, and more worse it introduces horrible boot delay + * issue because synchronize_rcu() is implied in lockdep_unregister_key which + * is called for each hctx release. SCSI probing may synchronously create and + * destroy lots of MQ request_queues for non-existent devices, and some robot + * test kernel always enable lockdep option. It is observed that more than half + * an hour is taken during SCSI MQ probe with per-fq lock class. + */ +void blk_mq_hctx_set_fq_lock_class(struct blk_mq_hw_ctx *hctx, + struct lock_class_key *key) +{ + lockdep_set_class(&hctx->fq->mq_flush_lock, key); +} +EXPORT_SYMBOL_GPL(blk_mq_hctx_set_fq_lock_class); diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h index 794b2a33a2c3..5f639240760e 100644 --- a/include/linux/blk-mq.h +++ b/include/linux/blk-mq.h @@ -5,6 +5,7 @@ #include #include #include +#include struct blk_mq_tags; struct blk_flush_queue; @@ -594,5 +595,7 @@ static inline void blk_mq_cleanup_rq(struct request *rq) } blk_qc_t blk_mq_submit_bio(struct bio *bio); +void blk_mq_hctx_set_fq_lock_class(struct blk_mq_hw_ctx *hctx, + struct lock_class_key *key); #endif -- 2.25.4 _______________________________________________ Linux-nvme mailing list Linux-nvme@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-nvme