6.1-stable review patch. If anyone has any objections, please let me know.
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From: Yu Zhao yuzhao@google.com
commit 8b671fe1a879923ecfb72dda6caf01460dd885ef upstream.
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 Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- mm/vmscan.c | 1 - 1 file changed, 1 deletion(-)
--- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -5065,7 +5065,6 @@ 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);