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authorJianchao Wang <jianchao.w.wang@oracle.com>2018-08-21 15:15:04 +0800
committerJens Axboe <axboe@kernel.dk>2018-08-21 09:02:56 -0600
commitf5bbbbe4d63577026f908a809f22f5fd5a90ea1f (patch)
treea6d8a1e7329b4160285b79a0565a45b53a2809f6 /block
parentd48ece209f82c9ce07be942441b53d3fa3664936 (diff)
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blk-mq: sync the update nr_hw_queues with blk_mq_queue_tag_busy_iter
For blk-mq, part_in_flight/rw will invoke blk_mq_in_flight/rw to account the inflight requests. It will access the queue_hw_ctx and nr_hw_queues w/o any protection. When updating nr_hw_queues and blk_mq_in_flight/rw occur concurrently, panic comes up. Before update nr_hw_queues, the q will be frozen. So we could use q_usage_counter to avoid the race. percpu_ref_is_zero is used here so that we will not miss any in-flight request. The access to nr_hw_queues and queue_hw_ctx in blk_mq_queue_tag_busy_iter are under rcu critical section, __blk_mq_update_nr_hw_queues could use synchronize_rcu to ensure the zeroed q_usage_counter to be globally visible. Signed-off-by: Jianchao Wang <jianchao.w.wang@oracle.com> Reviewed-by: Ming Lei <ming.lei@redhat.com> Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'block')
-rw-r--r--block/blk-mq-tag.c14
-rw-r--r--block/blk-mq.c4
2 files changed, 17 insertions, 1 deletions
diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c
index c0c4e63583ae..8c5cc115b3f8 100644
--- a/block/blk-mq-tag.c
+++ b/block/blk-mq-tag.c
@@ -320,6 +320,18 @@ void blk_mq_queue_tag_busy_iter(struct request_queue *q, busy_iter_fn *fn,
struct blk_mq_hw_ctx *hctx;
int i;
+ /*
+ * __blk_mq_update_nr_hw_queues will update the nr_hw_queues and
+ * queue_hw_ctx after freeze the queue. So we could use q_usage_counter
+ * to avoid race with it. __blk_mq_update_nr_hw_queues will users
+ * synchronize_rcu to ensure all of the users go out of the critical
+ * section below and see zeroed q_usage_counter.
+ */
+ rcu_read_lock();
+ if (percpu_ref_is_zero(&q->q_usage_counter)) {
+ rcu_read_unlock();
+ return;
+ }
queue_for_each_hw_ctx(q, hctx, i) {
struct blk_mq_tags *tags = hctx->tags;
@@ -335,7 +347,7 @@ void blk_mq_queue_tag_busy_iter(struct request_queue *q, busy_iter_fn *fn,
bt_for_each(hctx, &tags->breserved_tags, fn, priv, true);
bt_for_each(hctx, &tags->bitmap_tags, fn, priv, false);
}
-
+ rcu_read_unlock();
}
static int bt_alloc(struct sbitmap_queue *bt, unsigned int depth,
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 9c8c8c71a13f..81cb84b17b73 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -2977,6 +2977,10 @@ static void __blk_mq_update_nr_hw_queues(struct blk_mq_tag_set *set,
list_for_each_entry(q, &set->tag_list, tag_set_list)
blk_mq_freeze_queue(q);
/*
+ * Sync with blk_mq_queue_tag_busy_iter.
+ */
+ synchronize_rcu();
+ /*
* Switch IO scheduler to 'none', cleaning up the data associated
* with the previous scheduler. We will switch back once we are done
* updating the new sw to hw queue mappings.