From 316ad076e0d35d0844ba3c79cb8c9639d3dbf7f8 Mon Sep 17 00:00:00 2001 From: Chengming Zhou Date: Thu, 13 Apr 2023 14:28:04 +0800 Subject: [PATCH] blk-stat: fix QUEUE_FLAG_STATS clear 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: # v5.17+ Signed-off-by: Chengming Zhou Acked-by: Tejun Heo Link: https://lore.kernel.org/r/20230413062805.2081970-1-chengming.zhou@linux.dev Signed-off-by: Jens Axboe Signed-off-by: Greg Kroah-Hartman --- block/blk-stat.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/block/blk-stat.c b/block/blk-stat.c index 2ea01b5c1aca..da9407b7d4ab 100644 --- a/block/blk-stat.c +++ b/block/blk-stat.c @@ -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); }