During testing it has been detected, that it is possible to get div by zero error in bdi_set_min_bytes. The error is caused by the function bdi_ratio_from_pages(). bdi_ratio_from_pages() calls global_dirty_limits. If the dirty threshold is 0, the div by zero is raised. This can happen if the root user is setting: echo 0 > /proc/sys/vm/dirty_ratio The following is a test case: echo 0 > /proc/sys/vm/dirty_ratio cd /sys/class/bdi/<device> echo 1 > strict_limit echo 8192 > min_bytes ==> error is raised. The problem is addressed by returning -EINVAL if dirty_ratio or dirty_bytes is set to 0. Reported-by: cheung wall <zzqq0103.hey@xxxxxxxxx> Closes: https://lore.kernel.org/linux-mm/87pll35yd0.fsf@xxxxxxxxxxxx/T/#t Signed-off-by: Stefan Roesch <shr@xxxxxxxxxxxx> --- Changes in V2: - check for -EINVAL in bdi_set_min_bytes() - check for -EINVAL in bdi_set_max_bytes() --- mm/page-writeback.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/mm/page-writeback.c b/mm/page-writeback.c index d213ead95675..fcc486e0d5c2 100644 --- a/mm/page-writeback.c +++ b/mm/page-writeback.c @@ -692,6 +692,8 @@ static unsigned long bdi_ratio_from_pages(unsigned long pages) unsigned long ratio; global_dirty_limits(&background_thresh, &dirty_thresh); + if (!dirty_thresh) + return -EINVAL; ratio = div64_u64(pages * 100ULL * BDI_RATIO_SCALE, dirty_thresh); return ratio; @@ -797,6 +799,8 @@ int bdi_set_min_bytes(struct backing_dev_info *bdi, u64 min_bytes) return ret; min_ratio = bdi_ratio_from_pages(pages); + if (min_ratio == -EINVAL) + return -EINVAL; return __bdi_set_min_ratio(bdi, min_ratio); } @@ -816,6 +820,8 @@ int bdi_set_max_bytes(struct backing_dev_info *bdi, u64 max_bytes) return ret; max_ratio = bdi_ratio_from_pages(pages); + if (max_ratio == -EINVAL) + return -EINVAL; return __bdi_set_max_ratio(bdi, max_ratio); } base-commit: fbfd64d25c7af3b8695201ebc85efe90be28c5a3 -- 2.47.1
