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...

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@google.com 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@google.com Fixes: 359a5e1416ca ("mm: multi-gen LRU: retry folios written back while isolated") Reported-by: Wei Xu weixugc@google.com Signed-off-by: Yu Zhao yuzhao@google.com Cc: Alexander Motin mav@ixsystems.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

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@google.com 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