[v2,1/2] blk-stat: fix QUEUE_FLAG_STATS clear
Commit Message
From: Chengming Zhou <zhouchengming@bytedance.com>
We need to set QUEUE_FLAG_STATS for two cases:
1. blk_stat_enable_accounting()
2. blk_stat_add_callback()
So we should clear it only when ((q->stats->accounting == 0) &&
list_empty(&q->stats->callbacks)).
blk_stat_disable_accounting() only check if q->stats->accounting
is 0 before clear the flag, this patch fix it.
Also add list_empty(&q->stats->callbacks)) check when enable, or
the flag is already set.
The bug can be reproduced on kernel without BLK_DEV_THROTTLING
(since it unconditionally enable accounting, see the next patch).
# cat /sys/block/sr0/queue/scheduler
none mq-deadline [bfq]
# cat /sys/kernel/debug/block/sr0/state
SAME_COMP|IO_STAT|INIT_DONE|STATS|REGISTERED|NOWAIT|30
# echo none > /sys/block/sr0/queue/scheduler
# cat /sys/kernel/debug/block/sr0/state
SAME_COMP|IO_STAT|INIT_DONE|REGISTERED|NOWAIT
# cat /sys/block/sr0/queue/wbt_lat_usec
75000
We can see that after changing elevator from "bfq" to "none",
"STATS" flag is lost even though WBT callback still need it.
Fixes: 68497092bde9 ("block: make queue stat accounting a reference")
Cc: <stable@vger.kernel.org> # v5.17+
Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com>
Acked-by: Tejun Heo <tj@kernel.org>
---
block/blk-stat.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
Comments
On Thu, 13 Apr 2023 14:28:04 +0800, chengming.zhou@linux.dev wrote:
> We need to set QUEUE_FLAG_STATS for two cases:
> 1. blk_stat_enable_accounting()
> 2. blk_stat_add_callback()
>
> So we should clear it only when ((q->stats->accounting == 0) &&
> list_empty(&q->stats->callbacks)).
>
> [...]
Applied, thanks!
[1/2] blk-stat: fix QUEUE_FLAG_STATS clear
commit: 20de765f6d9da0c47b756429c60b41063b990a10
[2/2] blk-throttle: only enable blk-stat when BLK_DEV_THROTTLING_LOW
commit: 8e15dfbd9ae21e518979e3823e335073e725f445
Best regards,
@@ -190,7 +190,7 @@ void blk_stat_disable_accounting(struct request_queue *q)
unsigned long flags;
spin_lock_irqsave(&q->stats->lock, flags);
- if (!--q->stats->accounting)
+ if (!--q->stats->accounting && list_empty(&q->stats->callbacks))
blk_queue_flag_clear(QUEUE_FLAG_STATS, q);
spin_unlock_irqrestore(&q->stats->lock, flags);
}
@@ -201,7 +201,7 @@ void blk_stat_enable_accounting(struct request_queue *q)
unsigned long flags;
spin_lock_irqsave(&q->stats->lock, flags);
- if (!q->stats->accounting++)
+ if (!q->stats->accounting++ && list_empty(&q->stats->callbacks))
blk_queue_flag_set(QUEUE_FLAG_STATS, q);
spin_unlock_irqrestore(&q->stats->lock, flags);
}