20de765f6d
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>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.