The patch titled
Subject: mm-fix-div-by-zero-in-bdi_ratio_from_pages-v3
has been added to the -mm mm-hotfixes-unstable branch. Its filename is
mm-fix-div-by-zero-in-bdi_ratio_from_pages-v3.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-fix-div-by-zero-in-bdi_ratio_from_pages-v3.patch
This patch will later appear in the mm-hotfixes-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
Before you just go and hit "reply", please:
a) Consider who else should be cc'ed
b) Prefer to cc a suitable mailing list as well
c) Ideally: find the original patch on the mailing list and do a
reply-to-all to that, adding suitable additional cc's
*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
The -mm tree is included into linux-next via the mm-everything
branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there every 2-3 working days
------------------------------------------------------
From: Stefan Roesch <shr@xxxxxxxxxxxx>
Subject: mm-fix-div-by-zero-in-bdi_ratio_from_pages-v3
Date: Wed, 8 Jan 2025 22:34:11 -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.
Link: https://lkml.kernel.org/r/20250109063411.6591-1-shr@xxxxxxxxxxxx
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>
Cc: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/page-writeback.c | 12 ++++++------
1 file changed, 6 insertions(+), 6 deletions(-)
--- a/mm/page-writeback.c~mm-fix-div-by-zero-in-bdi_ratio_from_pages-v3
+++ a/mm/page-writeback.c
@@ -792,15 +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 == -EINVAL)
- return -EINVAL;
+ if (min_ratio < 0)
+ return min_ratio;
return __bdi_set_min_ratio(bdi, min_ratio);
}
@@ -813,15 +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 == -EINVAL)
- return -EINVAL;
+ 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
mm-fix-div-by-zero-in-bdi_ratio_from_pages.patch
mm-fix-div-by-zero-in-bdi_ratio_from_pages-v2.patch
mm-fix-div-by-zero-in-bdi_ratio_from_pages-v3.patch
