Commit 9a9f904d authored by Jingbo Xu's avatar Jingbo Xu Committed by Liu Shixin
Browse files

mm: fix arithmetic for bdi min_ratio 

mainline inclusion
from mainline-v6.7
commit e0646b7590084a5bf3b056d3ad871d9379d2c25a
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/IBE0E0

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=e0646b7590084a5bf3b056d3ad871d9379d2c25a

--------------------------------

Since now bdi->min_ratio is part per million, fix the wrong arithmetic.
Otherwise it will fail with -EINVAL when setting a reasonable min_ratio,
as it tries to set min_ratio to (min_ratio * BDI_RATIO_SCALE) in
percentage unit, which exceeds 100% anyway.

    # cat /sys/class/bdi/253\:0/min_ratio
    0
    # cat /sys/class/bdi/253\:0/max_ratio
    100
    # echo 1 > /sys/class/bdi/253\:0/min_ratio
    -bash: echo: write error: Invalid argument

Link: https://lkml.kernel.org/r/20231219142508.86265-2-jefflexu@linux.alibaba.com


Fixes: 8021fb32 ("mm: split off __bdi_set_min_ratio() function")
Signed-off-by: default avatarJingbo Xu <jefflexu@linux.alibaba.com>
Reported-by: default avatarJoseph Qi <joseph.qi@linux.alibaba.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Stefan Roesch <shr@devkernel.io>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLiu Shixin <liushixin2@huawei.com>
parent e419e9e8

mm/page-writeback.c

+0 −1
Original line number Diff line number Diff line
@@ -714,7 +714,6 @@ static int __bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ra 


	if (min_ratio > 100 * BDI_RATIO_SCALE)

		return -EINVAL;

	min_ratio *= BDI_RATIO_SCALE;



	spin_lock_bh(&bdi_lock);

	if (min_ratio > bdi->max_ratio) {