From: Yu Kuai <yukuai3@xxxxxxxxxx> Currently issue io can grab queue_lock three times from bfq_bio_merge(), bfq_limit_depth() and bfq_prepare_request(), the queue_lock is not necessary if icq is already created because both queue and ioc can't be freed before io issuing is done, hence remove the unnecessary queue_lock and use rcu to protect radix tree lookup. Noted this is also a prep patch to support request batch dispatching[1]. [1] https://lore.kernel.org/all/20250722072431.610354-1-yukuai1@xxxxxxxxxxxxxxx/ Signed-off-by: Yu Kuai <yukuai3@xxxxxxxxxx> Reviewed-by: Damien Le Moal <dlemoal@xxxxxxxxxx> Reviewed-by: Jan Kara <jack@xxxxxxx> --- changes from v2: - update comments; - add review tag from Jan and Damien; changes from v1: - modify ioc_lookup_icq() directly to get rid of queue_lock; block/bfq-iosched.c | 18 ++---------------- block/blk-ioc.c | 16 ++++++---------- 2 files changed, 8 insertions(+), 26 deletions(-) diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c index 0cb1e9873aab..f71ec0887733 100644 --- a/block/bfq-iosched.c +++ b/block/bfq-iosched.c @@ -454,17 +454,10 @@ static struct bfq_io_cq *icq_to_bic(struct io_cq *icq) */ static struct bfq_io_cq *bfq_bic_lookup(struct request_queue *q) { - struct bfq_io_cq *icq; - unsigned long flags; - if (!current->io_context) return NULL; - spin_lock_irqsave(&q->queue_lock, flags); - icq = icq_to_bic(ioc_lookup_icq(q)); - spin_unlock_irqrestore(&q->queue_lock, flags); - - return icq; + return icq_to_bic(ioc_lookup_icq(q)); } /* @@ -2457,15 +2450,8 @@ static bool bfq_bio_merge(struct request_queue *q, struct bio *bio, unsigned int nr_segs) { struct bfq_data *bfqd = q->elevator->elevator_data; - struct request *free = NULL; - /* - * bfq_bic_lookup grabs the queue_lock: invoke it now and - * store its return value for later use, to avoid nesting - * queue_lock inside the bfqd->lock. We assume that the bic - * returned by bfq_bic_lookup does not go away before - * bfqd->lock is taken. - */ struct bfq_io_cq *bic = bfq_bic_lookup(q); + struct request *free = NULL; bool ret; spin_lock_irq(&bfqd->lock); diff --git a/block/blk-ioc.c b/block/blk-ioc.c index ce82770c72ab..9fda3906e5f5 100644 --- a/block/blk-ioc.c +++ b/block/blk-ioc.c @@ -308,24 +308,23 @@ int __copy_io(unsigned long clone_flags, struct task_struct *tsk) #ifdef CONFIG_BLK_ICQ /** - * ioc_lookup_icq - lookup io_cq from ioc + * ioc_lookup_icq - lookup io_cq from ioc in io issue path * @q: the associated request_queue * * Look up io_cq associated with @ioc - @q pair from @ioc. Must be called - * with @q->queue_lock held. + * from io issue path, either return NULL if current issue io to @q for the + * first time, or return a valid icq. */ struct io_cq *ioc_lookup_icq(struct request_queue *q) { struct io_context *ioc = current->io_context; struct io_cq *icq; - lockdep_assert_held(&q->queue_lock); - /* * icq's are indexed from @ioc using radix tree and hint pointer, - * both of which are protected with RCU. All removals are done - * holding both q and ioc locks, and we're holding q lock - if we - * find a icq which points to us, it's guaranteed to be valid. + * both of which are protected with RCU, io issue path ensures that + * both request_queue and current task are valid, the found icq + * is guaranteed to be valid until the io is done. */ rcu_read_lock(); icq = rcu_dereference(ioc->icq_hint); @@ -419,10 +418,7 @@ struct io_cq *ioc_find_get_icq(struct request_queue *q) task_unlock(current); } else { get_io_context(ioc); - - spin_lock_irq(&q->queue_lock); icq = ioc_lookup_icq(q); - spin_unlock_irq(&q->queue_lock); } if (!icq) { -- 2.39.2
