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blk-stat: fix QUEUE_FLAG_STATS clear

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commit 20de765f6d9da0c47b756429c60b41063b990a10 upstream.

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>
Link: https://lore.kernel.org/r/20230413062805.2081970-1-chengming.zhou@linux.dev
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Chengming Zhou 2023-04-13 14:28:04 +08:00 committed by Greg Kroah-Hartman
parent 3285613127
commit 316ad076e0
1 changed files with 2 additions and 2 deletions
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4
block/blk-stat.c
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@ -189,7 +189,7 @@ 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);
}
@ -200,7 +200,7 @@ 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);
}