The patch titled
Subject: Revert "mm/writeback: fix possible divide-by-zero in wb_dirty_limits(), again"
has been added to the -mm mm-unstable branch. Its filename is
revert-mm-writeback-fix-possible-divide-by-zero-in-wb_dirty_limits-again.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/revert-mm-writeback-fix-possible-divide-by-zero-in-wb_dirty_limits-again.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Jan Kara <jack@xxxxxxx>
Subject: Revert "mm/writeback: fix possible divide-by-zero in wb_dirty_limits(), again"
Date: Fri, 21 Jun 2024 16:42:37 +0200
Patch series "mm: Avoid possible overflows in dirty throttling".
Dirty throttling logic assumes dirty limits in page units fit into
32-bits. This patch series makes sure this is true (see patch 2/2 for
more details).
This patch (of 2):
This reverts commit 9319b647902cbd5cc884ac08a8a6d54ce111fc78.
The commit is broken in several ways. Firstly, the removed (u64) cast
from the multiplication will introduce a multiplication overflow on 32-bit
archs if wb_thresh * bg_thresh >= 1<<32 (which is actually common - the
default settings with 4GB of RAM will trigger this). Secondly, the
div64_u64() is unnecessarily expensive on 32-bit archs. We have
div64_ul() in case we want to be safe & cheap. Thirdly, if dirty
thresholds are larger than 1<<32 pages, then dirty balancing is going to
blow up in many other spectacular ways anyway so trying to fix one
possible overflow is just moot.
Link: https://lkml.kernel.org/r/20240621144017.30993-1-jack@xxxxxxx
Link: https://lkml.kernel.org/r/20240621144246.11148-1-jack@xxxxxxx
Fixes: 9319b647902c ("mm/writeback: fix possible divide-by-zero in wb_dirty_limits(), again")
Signed-off-by: Jan Kara <jack@xxxxxxx>
Cc: Zach O'Keefe <zokeefe@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/page-writeback.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- a/mm/page-writeback.c~revert-mm-writeback-fix-possible-divide-by-zero-in-wb_dirty_limits-again
+++ a/mm/page-writeback.c
@@ -1683,7 +1683,7 @@ static inline void wb_dirty_limits(struc
*/
dtc->wb_thresh = __wb_calc_thresh(dtc, dtc->thresh);
dtc->wb_bg_thresh = dtc->thresh ?
- div64_u64(dtc->wb_thresh * dtc->bg_thresh, dtc->thresh) : 0;
+ div_u64((u64)dtc->wb_thresh * dtc->bg_thresh, dtc->thresh) : 0;
/*
* In order to avoid the stacked BDI deadlock we need
_
Patches currently in -mm which might be from jack@xxxxxxx are
ocfs2-fix-dio-failure-due-to-insufficient-transaction-credits.patch
revert-mm-writeback-fix-possible-divide-by-zero-in-wb_dirty_limits-again.patch
mm-avoid-overflows-in-dirty-throttling-logic.patch
