linux-kernel - [PATCH v2 1/2] mm: fix arithmetic for bdi min

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Date: Tue, 19 Dec 2023 10:42:45 +0800
From: Jingbo Xu <jefflexu@...ux.alibaba.com>
To: shr@...kernel.io,
	akpm@...ux-foundation.org
Cc: linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	joseph.qi@...ux.alibaba.com,
	linux-fsdevel@...r.kernel.org,
	linux-block@...r.kernel.org
Subject: [PATCH v2 1/2] mm: fix arithmetic for bdi min_ratio

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

Fixes: 8021fb3232f2 ("mm: split off __bdi_set_min_ratio() function")
Reported-by: Joseph Qi <joseph.qi@...ux.alibaba.com>
Signed-off-by: Jingbo Xu <jefflexu@...ux.alibaba.com>
---
 mm/page-writeback.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index ee2fd6a6af40..2140382dd768 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -692,7 +692,6 @@ 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) {
-- 
2.19.1.6.gb485710b