On 6/9/23 2:51?AM, Yu Kuai wrote:
> From: Yu Kuai <yukuai3@xxxxxxxxxx>
>
> In __blk_mq_tag_busy/idle(), updating 'active_queues' and calculating
> 'wake_batch' is not atomic:
>
> t1: t2:
> _blk_mq_tag_busy blk_mq_tag_busy
> inc active_queues
> // assume 1->2
> inc active_queues
> // 2 -> 3
> blk_mq_update_wake_batch
> // calculate based on 3
> blk_mq_update_wake_batch
> /* calculate based on 2, while active_queues is actually 3. */
>
> Fix this problem by protecting them wih 'tags->lock', this is not a hot
> path, so performance should not be concerned.
>
> Fixes: 180dccb0dba4 ("blk-mq: fix tag_get wait task can't be awakened")
> Signed-off-by: Yu Kuai <yukuai3@xxxxxxxxxx>
> ---
> block/blk-mq-tag.c | 6 ++++--
> 1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c
> index dfd81cab5788..43fe523f39c7 100644
> --- a/block/blk-mq-tag.c
> +++ b/block/blk-mq-tag.c
> @@ -55,9 +55,10 @@ void __blk_mq_tag_busy(struct blk_mq_hw_ctx *hctx)
> return;
> }
>
> + spin_lock_irq(&hctx->tags->lock);
> users = atomic_inc_return(&hctx->tags->active_queues);
> -
> blk_mq_update_wake_batch(hctx->tags, users);
> + spin_unlock_irq(&hctx->tags->lock);
> }
>
> /*
> @@ -90,9 +91,10 @@ void __blk_mq_tag_idle(struct blk_mq_hw_ctx *hctx)
> return;
> }
>
> + spin_lock_irq(&tags->lock);
> users = atomic_dec_return(&tags->active_queues);
> -
> blk_mq_update_wake_batch(tags, users);
> + spin_unlock_irq(&tags->lock);
>
> blk_mq_tag_wakeup_all(tags, false);
> }
>From a quick look, these are the only manipulators of active_queues.
If we're under the tags lock, why do they still need to be atomics?
--
Jens Axboe
