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mm: rework calculation of bdi_min_ratio in bdi_set_min_ratio

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In function bdi_set_min_ratio, min_ratio is unsigned int, it will
result underflow when setting min_ratio below bdi->min_ratio, it
is confusing. Rework it, no functional change.

Link: https://lkml.kernel.org/r/20220422095159.2858305-1-chenwandun@huawei.com
Signed-off-by: Chen Wandun <chenwandun@huawei.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Chen Wandun
2022-04-28 23:15:57 -07:00
committed by akpm
parent c7c4ab8596
commit 21f0dd88f2
1 changed files with 12 additions and 5 deletions
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17
mm/page-writeback.c
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@@ -650,18 +650,25 @@ static unsigned int bdi_min_ratio;
int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio) int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio)
{ {
unsigned int delta;
int ret = 0; int ret = 0;
spin_lock_bh(&bdi_lock); spin_lock_bh(&bdi_lock);
if (min_ratio > bdi->max_ratio) { if (min_ratio > bdi->max_ratio) {
ret = -EINVAL; ret = -EINVAL;
} else { } else {
min_ratio -= bdi->min_ratio; if (min_ratio < bdi->min_ratio) {
if (bdi_min_ratio + min_ratio < 100) { delta = bdi->min_ratio - min_ratio;
bdi_min_ratio += min_ratio; bdi_min_ratio -= delta;
bdi->min_ratio += min_ratio; bdi->min_ratio = min_ratio;
} else { } else {
ret = -EINVAL; delta = min_ratio - bdi->min_ratio;
if (bdi_min_ratio + delta < 100) {
bdi_min_ratio += delta;
bdi->min_ratio = min_ratio;
} else {
ret = -EINVAL;
}
} }
} }
spin_unlock_bh(&bdi_lock); spin_unlock_bh(&bdi_lock);