From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Date: Fri, 7 Apr 2017 17:46:24 +0800 From: Ming Lei To: Bart Van Assche Cc: Jens Axboe , linux-block@vger.kernel.org, Christoph Hellwig , Hannes Reinecke Subject: Re: [PATCH v3 1/5] blk-mq: Make it safe to use RCU to iterate over blk_mq_tag_set.tag_list Message-ID: <20170407094623.GD27631@ming.t460p> References: <20170406181050.12137-1-bart.vanassche@sandisk.com> <20170406181050.12137-2-bart.vanassche@sandisk.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <20170406181050.12137-2-bart.vanassche@sandisk.com> List-ID: On Thu, Apr 06, 2017 at 11:10:46AM -0700, Bart Van Assche wrote: > Since the next patch in this series will use RCU to iterate over > tag_list, make this safe. Add lockdep_assert_held() statements > in functions that iterate over tag_list to make clear that using > list_for_each_entry() instead of list_for_each_entry_rcu() is > fine in these functions. > > Signed-off-by: Bart Van Assche > Cc: Christoph Hellwig > Cc: Hannes Reinecke > --- > block/blk-mq.c | 6 ++++++ > 1 file changed, 6 insertions(+) > > diff --git a/block/blk-mq.c b/block/blk-mq.c > index f7cd3208bcdf..b5580b09b4a5 100644 > --- a/block/blk-mq.c > +++ b/block/blk-mq.c > @@ -2076,6 +2076,8 @@ static void blk_mq_update_tag_set_depth(struct blk_mq_tag_set *set, bool shared) > { > struct request_queue *q; > > + lockdep_assert_held(&set->tag_list_lock); > + > list_for_each_entry(q, &set->tag_list, tag_set_list) { > blk_mq_freeze_queue(q); > queue_set_hctx_shared(q, shared); > @@ -2096,6 +2098,8 @@ static void blk_mq_del_queue_tag_set(struct request_queue *q) > blk_mq_update_tag_set_depth(set, false); > } > mutex_unlock(&set->tag_list_lock); > + > + synchronize_rcu(); Looks synchronize_rcu() is only needed in deletion path, so it can be moved to blk_mq_del_queue_tag_set(). Also list_del_init/list_add_tail() need to be replaced with RCU safe version in functions operating &set->tag_list. > } > > static void blk_mq_add_queue_tag_set(struct blk_mq_tag_set *set, > @@ -2601,6 +2605,8 @@ void blk_mq_update_nr_hw_queues(struct blk_mq_tag_set *set, int nr_hw_queues) > { > struct request_queue *q; > > + lockdep_assert_held(&set->tag_list_lock); > + > if (nr_hw_queues > nr_cpu_ids) > nr_hw_queues = nr_cpu_ids; > if (nr_hw_queues < 1 || nr_hw_queues == set->nr_hw_queues) > -- > 2.12.0 > -- Ming