| Message ID | 20180925163620.11911-1-keith.busch@intel.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [PATCHv2] blk-mq: Allow blocking queue tag iter callbacks | expand |
Hi Keith On 09/26/2018 12:36 AM, Keith Busch wrote: > A recent commit runs tag iterator callbacks under the rcu read lock, > but existing callbacks do not satisfy the non-blocking requirement. > The commit intended to prevent an iterator from accessing a queue that's > being modified. This patch fixes the original issue by taking a queue > reference instead of reading it, which allows callbacks to make blocking > calls. > > Fixes: f5bbbbe4d6357 ("blk-mq: sync the update nr_hw_queues with blk_mq_queue_tag_busy_iter") > Cc: Jianchao Wang <jianchao.w.wang@oracle.com> > Signed-off-by: Keith Busch <keith.busch@intel.com> > --- > v1 -> v2: > > Leave the iterator interface as-is, making this change transparent > to the callers. This will increment the queue usage counter in the > timeout path twice, which is harmless. > This is OK to me. Acked-by: Jianchao Wang <jianchao.w.wang@oracle.com> > Changelog. > > block/blk-mq-tag.c | 13 ++++--------- > 1 file changed, 4 insertions(+), 9 deletions(-) > > diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c > index 94e1ed667b6e..41317c50a446 100644 > --- a/block/blk-mq-tag.c > +++ b/block/blk-mq-tag.c > @@ -322,16 +322,11 @@ void blk_mq_queue_tag_busy_iter(struct request_queue *q, busy_iter_fn *fn, > > /* > * __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. > + * queue_hw_ctx after freeze the queue, so we use q_usage_counter > + * to avoid race with it. > */ > - rcu_read_lock(); > - if (percpu_ref_is_zero(&q->q_usage_counter)) { > - rcu_read_unlock(); > + if (!percpu_ref_tryget(&q->q_usage_counter)) > return; > - } > > queue_for_each_hw_ctx(q, hctx, i) { > struct blk_mq_tags *tags = hctx->tags; > @@ -347,7 +342,7 @@ 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(); > + blk_queue_exit(q); > } > > static int bt_alloc(struct sbitmap_queue *bt, unsigned int depth, >
On 9/25/18 10:36 AM, Keith Busch wrote: > A recent commit runs tag iterator callbacks under the rcu read lock, > but existing callbacks do not satisfy the non-blocking requirement. > The commit intended to prevent an iterator from accessing a queue that's > being modified. This patch fixes the original issue by taking a queue > reference instead of reading it, which allows callbacks to make blocking > calls. Thanks Keith, queued up for 4.19.
diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c index 94e1ed667b6e..41317c50a446 100644 --- a/block/blk-mq-tag.c +++ b/block/blk-mq-tag.c @@ -322,16 +322,11 @@ void blk_mq_queue_tag_busy_iter(struct request_queue *q, busy_iter_fn *fn, /* * __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. + * queue_hw_ctx after freeze the queue, so we use q_usage_counter + * to avoid race with it. */ - rcu_read_lock(); - if (percpu_ref_is_zero(&q->q_usage_counter)) { - rcu_read_unlock(); + if (!percpu_ref_tryget(&q->q_usage_counter)) return; - } queue_for_each_hw_ctx(q, hctx, i) { struct blk_mq_tags *tags = hctx->tags; @@ -347,7 +342,7 @@ 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(); + blk_queue_exit(q); } static int bt_alloc(struct sbitmap_queue *bt, unsigned int depth,
A recent commit runs tag iterator callbacks under the rcu read lock, but existing callbacks do not satisfy the non-blocking requirement. The commit intended to prevent an iterator from accessing a queue that's being modified. This patch fixes the original issue by taking a queue reference instead of reading it, which allows callbacks to make blocking calls. Fixes: f5bbbbe4d6357 ("blk-mq: sync the update nr_hw_queues with blk_mq_queue_tag_busy_iter") Cc: Jianchao Wang <jianchao.w.wang@oracle.com> Signed-off-by: Keith Busch <keith.busch@intel.com> --- v1 -> v2: Leave the iterator interface as-is, making this change transparent to the callers. This will increment the queue usage counter in the timeout path twice, which is harmless. Changelog. block/blk-mq-tag.c | 13 ++++--------- 1 file changed, 4 insertions(+), 9 deletions(-)