Commit 21f0dd88 authored by Chen Wandun's avatar Chen Wandun Committed by Andrew Morton
Browse files

mm: rework calculation of bdi_min_ratio in bdi_set_min_ratio 

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: default avatarChen Wandun <chenwandun@huawei.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Jens Axboe <axboe@kernel.dk>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent c7c4ab85

mm/page-writeback.c

+12 −5
Original line number Diff line number Diff line
@@ -650,20 +650,27 @@ static unsigned int bdi_min_ratio; 


int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio)

{

	unsigned int delta;

	int ret = 0;



	spin_lock_bh(&bdi_lock);

	if (min_ratio > bdi->max_ratio) {

		ret = -EINVAL;

	} else {

		min_ratio -= bdi->min_ratio;

		if (bdi_min_ratio + min_ratio < 100) {

			bdi_min_ratio += min_ratio;

			bdi->min_ratio += min_ratio;

		if (min_ratio < bdi->min_ratio) {

			delta = bdi->min_ratio - min_ratio;

			bdi_min_ratio -= delta;

			bdi->min_ratio = min_ratio;

		} else {

			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);



	return ret;