* [PATCH -next] blk-mq: fix potential io hang by wrong 'wake_batch'
@ 2023-06-09 8:51 Yu Kuai
2023-06-09 17:41 ` Jens Axboe
0 siblings, 1 reply; 3+ messages in thread
From: Yu Kuai @ 2023-06-09 8:51 UTC (permalink / raw)
To: jack, axboe, andriy.shevchenko, qiulaibin
Cc: linux-block, linux-kernel, yukuai3, yukuai1, yi.zhang, yangerkun
From: Yu Kuai <yukuai3@huawei.com>
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@huawei.com>
---
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);
}
--
2.39.2
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH -next] blk-mq: fix potential io hang by wrong 'wake_batch'
2023-06-09 8:51 [PATCH -next] blk-mq: fix potential io hang by wrong 'wake_batch' Yu Kuai
@ 2023-06-09 17:41 ` Jens Axboe
2023-06-10 2:26 ` Yu Kuai
0 siblings, 1 reply; 3+ messages in thread
From: Jens Axboe @ 2023-06-09 17:41 UTC (permalink / raw)
To: Yu Kuai, jack, andriy.shevchenko, qiulaibin
Cc: linux-block, linux-kernel, yukuai3, yi.zhang, yangerkun
On 6/9/23 2:51?AM, Yu Kuai wrote:
> From: Yu Kuai <yukuai3@huawei.com>
>
> 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@huawei.com>
> ---
> 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
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH -next] blk-mq: fix potential io hang by wrong 'wake_batch'
2023-06-09 17:41 ` Jens Axboe
@ 2023-06-10 2:26 ` Yu Kuai
0 siblings, 0 replies; 3+ messages in thread
From: Yu Kuai @ 2023-06-10 2:26 UTC (permalink / raw)
To: Jens Axboe, Yu Kuai, jack, andriy.shevchenko, qiulaibin
Cc: linux-block, linux-kernel, yi.zhang, yangerkun, yukuai (C)
Hi,
在 2023/06/10 1:41, Jens Axboe 写道:
>>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?
>
Yes, 'active_queues' doesn't need to be atomic any more.
Thanks,
Kuai
^ permalink raw reply [flat|nested] 3+ messages in thread
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2023-06-09 8:51 [PATCH -next] blk-mq: fix potential io hang by wrong 'wake_batch' Yu Kuai
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