[PATCH v2 2/5] blk-mq: Make it safe to use RCU to iterate over blk_mq_tag_set.tag_list

Bart Van Assche
2017-04-03T23:22:25Z

A later patch in this series will namely use RCU to iterate over
this list.

Signed-off-by: Bart Van Assche <bart.vanassche@sandisk.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Hannes Reinecke <hare@suse.com>
Cc: Martin K. Petersen <martin.petersen@oracle.com>
Cc: James Bottomley <James.Bottomley@HansenPartnership.com>
---
block/blk-mq.c | 6 ++++++
1 file changed, 6 insertions(+)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 061fc2cc88d3..8fb983e6e2e4 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -2093,6 +2093,8 @@ 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);
@@ -2113,6 +2115,8 @@ 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();
}

static void blk_mq_add_queue_tag_set(struct blk_mq_tag_set *set,
@@ -2618,6 +2622,8 @@ 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