The quilt patch titled
Subject: mm: fix div by zero in bdi_ratio_from_pages
has been removed from the -mm tree. Its filename was
mm-fix-div-by-zero-in-bdi_ratio_from_pages.patch
This patch was dropped because it was merged into the mm-hotfixes-stable branch
of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
------------------------------------------------------
From: Stefan Roesch <shr@xxxxxxxxxxxx>
Subject: mm: fix div by zero in bdi_ratio_from_pages
Date: Fri, 3 Jan 2025 17:20:37 -0800
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.
[shr@xxxxxxxxxxxx: check for -EINVAL in bdi_set_min_bytes() and bdi_set_max_bytes()]
Link: https://lkml.kernel.org/r/20250108014723.166637-1-shr@xxxxxxxxxxxx
[shr@xxxxxxxxxxxx: v3]
Link: https://lkml.kernel.org/r/20250109063411.6591-1-shr@xxxxxxxxxxxx
Link: https://lkml.kernel.org/r/20250104012037.159386-1-shr@xxxxxxxxxxxx
Signed-off-by: Stefan Roesch <shr@xxxxxxxxxxxx>
Reported-by: cheung wall <zzqq0103.hey@xxxxxxxxx>
Closes: https://lore.kernel.org/linux-mm/87pll35yd0.fsf@xxxxxxxxxxxx/T/#t
Acked-by: David Hildenbrand <david@xxxxxxxxxx>
Cc: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Cc: Qiang Zhang <zzqq0103.hey@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/page-writeback.c | 10 ++++++++--
1 file changed, 8 insertions(+), 2 deletions(-)
--- a/mm/page-writeback.c~mm-fix-div-by-zero-in-bdi_ratio_from_pages
+++ a/mm/page-writeback.c
@@ -692,6 +692,8 @@ static unsigned long bdi_ratio_from_page
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;
@@ -790,13 +792,15 @@ int bdi_set_min_bytes(struct backing_dev
{
int ret;
unsigned long pages = min_bytes >> PAGE_SHIFT;
- unsigned long min_ratio;
+ long min_ratio;
ret = bdi_check_pages_limit(pages);
if (ret)
return ret;
min_ratio = bdi_ratio_from_pages(pages);
+ if (min_ratio < 0)
+ return min_ratio;
return __bdi_set_min_ratio(bdi, min_ratio);
}
@@ -809,13 +813,15 @@ int bdi_set_max_bytes(struct backing_dev
{
int ret;
unsigned long pages = max_bytes >> PAGE_SHIFT;
- unsigned long max_ratio;
+ long max_ratio;
ret = bdi_check_pages_limit(pages);
if (ret)
return ret;
max_ratio = bdi_ratio_from_pages(pages);
+ if (max_ratio < 0)
+ return max_ratio;
return __bdi_set_max_ratio(bdi, max_ratio);
}
_
Patches currently in -mm which might be from shr@xxxxxxxxxxxx are
