This is a note to let you know that I've just added the patch titled
blk-stat: fix QUEUE_FLAG_STATS clear
to the 6.2-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
blk-stat-fix-queue_flag_stats-clear.patch
and it can be found in the queue-6.2 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 20de765f6d9da0c47b756429c60b41063b990a10 Mon Sep 17 00:00:00 2001
From: Chengming Zhou <zhouchengming@xxxxxxxxxxxxx>
Date: Thu, 13 Apr 2023 14:28:04 +0800
Subject: blk-stat: fix QUEUE_FLAG_STATS clear
From: Chengming Zhou <zhouchengming@xxxxxxxxxxxxx>
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@xxxxxxxxxxxxxxx> # v5.17+
Signed-off-by: Chengming Zhou <zhouchengming@xxxxxxxxxxxxx>
Acked-by: Tejun Heo <tj@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20230413062805.2081970-1-chengming.zhou@xxxxxxxxx
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
block/blk-stat.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
--- a/block/blk-stat.c
+++ b/block/blk-stat.c
@@ -189,7 +189,7 @@ void blk_stat_disable_accounting(struct
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 r
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);
}
Patches currently in stable-queue which might be from zhouchengming@xxxxxxxxxxxxx are
queue-6.2/blk-stat-fix-queue_flag_stats-clear.patch
