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blk-mq: add new API of blk_mq_hctx_set_fq_lock_class

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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'.

Tested-by: Kashyap Desai <kashyap.desai@broadcom.com>
Reported-by: Qian Cai <cai@redhat.com>
Cc: Sumit Saxena <sumit.saxena@broadcom.com>
Cc: John Garry <john.garry@huawei.com>
Cc: Kashyap Desai <kashyap.desai@broadcom.com>
Cc: Bart Van Assche <bvanassche@acm.org>
Cc: Hannes Reinecke <hare@suse.de>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Ming Lei 2020-12-03 09:26:36 +08:00 • committed by Jens Axboe
parent cc29e1bf0d
commit fb01a2932e
2 changed files with 28 additions and 0 deletions
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25
block/blk-flush.c
View file

@ -490,3 +490,28 @@ void blk_free_flush_queue(struct blk_flush_queue *fq)
kfree(fq->flush_rq); kfree(fq->flush_rq);
kfree(fq); 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);

3
include/linux/blk-mq.h
View file

@ -5,6 +5,7 @@
#include <linux/blkdev.h> #include <linux/blkdev.h>
#include <linux/sbitmap.h> #include <linux/sbitmap.h>
#include <linux/srcu.h> #include <linux/srcu.h>
#include <linux/lockdep.h>
struct blk_mq_tags; struct blk_mq_tags;
struct blk_flush_queue; 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); 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 #endif