| Message ID | 1534749606-7311-3-git-send-email-jianchao.w.wang@oracle.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | fixes for the updating nr_hw_queues | expand |
On Mon, Aug 20, 2018 at 3:18 PM Jianchao Wang <jianchao.w.wang@oracle.com> wrote: > > 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> > --- > block/blk-mq-tag.c | 14 +++++++++++++- > block/blk-mq.c | 5 ++++- > 2 files changed, 17 insertions(+), 2 deletions(-) > > diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c > index c0c4e63..8c5cc11 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 7b99477..fb56bae 100644 > --- a/block/blk-mq.c > +++ b/block/blk-mq.c > @@ -2905,7 +2905,10 @@ 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_in_flight and blk_mq_queue_tag_busy_iter. > + */ > + synchronize_rcu(); > /* > * switch io scheduler to NULL to clean up the data in it. > * will get it back after update mapping between cpu and hw queues. > -- > 2.7.4 > Reviewed-by: Ming Lei <ming.lei@redhat.com> Thanks, Ming Lei
diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c index c0c4e63..8c5cc11 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 7b99477..fb56bae 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -2905,7 +2905,10 @@ 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_in_flight and blk_mq_queue_tag_busy_iter. + */ + synchronize_rcu(); /* * switch io scheduler to NULL to clean up the data in it. * will get it back after update mapping between cpu and hw queues.
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> --- block/blk-mq-tag.c | 14 +++++++++++++- block/blk-mq.c | 5 ++++- 2 files changed, 17 insertions(+), 2 deletions(-)