The patch titled
Subject: mm/mglru: fix div-by-zero in vmpressure_calc_level()
has been added to the -mm mm-unstable branch. Its filename is
mm-mglru-fix-div-by-zero-in-vmpressure_calc_level.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-mglru-fix-div-by-zero-in-vmpressure_calc_level.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: Yu Zhao <yuzhao@xxxxxxxxxx>
Subject: mm/mglru: fix div-by-zero in vmpressure_calc_level()
Date: Thu, 11 Jul 2024 13:19:56 -0600
evict_folios() uses a second pass to reclaim folios that have gone through
page writeback and become clean before it finishes the first pass, since
folio_rotate_reclaimable() cannot handle those folios due to the
isolation.
The second pass tries to avoid potential double counting by deducting
scan_control->nr_scanned. However, this can result in underflow of
nr_scanned, under a condition where shrink_folio_list() does not increment
nr_scanned, i.e., when folio_trylock() fails.
The underflow can cause the divisor, i.e., scale=scanned+reclaimed in
vmpressure_calc_level(), to become zero, resulting in the following crash:
[exception RIP: vmpressure_work_fn+101]
process_one_work at ffffffffa3313f2b
Since scan_control->nr_scanned has no established semantics, the potential
double counting has minimal risks. Therefore, fix the problem by not
deducting scan_control->nr_scanned in evict_folios().
Link: https://lkml.kernel.org/r/20240711191957.939105-1-yuzhao@xxxxxxxxxx
Fixes: 359a5e1416ca ("mm: multi-gen LRU: retry folios written back while isolated")
Reported-by: Wei Xu <weixugc@xxxxxxxxxx>
Signed-off-by: Yu Zhao <yuzhao@xxxxxxxxxx>
Cc: Alexander Motin <mav@xxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/vmscan.c | 1 -
1 file changed, 1 deletion(-)
--- a/mm/vmscan.c~mm-mglru-fix-div-by-zero-in-vmpressure_calc_level
+++ a/mm/vmscan.c
@@ -4597,7 +4597,6 @@ retry:
/* retry folios that may have missed folio_rotate_reclaimable() */
list_move(&folio->lru, &clean);
- sc->nr_scanned -= folio_nr_pages(folio);
}
spin_lock_irq(&lruvec->lru_lock);
_
Patches currently in -mm which might be from yuzhao@xxxxxxxxxx are
mm-truncate-batch-clear-shadow-entries.patch
mm-truncate-batch-clear-shadow-entries-v2.patch
mm-mglru-fix-div-by-zero-in-vmpressure_calc_level.patch
mm-mglru-fix-overshooting-shrinker-memory.patch
