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 (cherry picked from commit 8b671fe1a879923ecfb72dda6caf01460dd885ef) --- mm/vmscan.c | 1 - 1 file changed, 1 deletion(-)
diff --git a/mm/vmscan.c b/mm/vmscan.c index e9d4c1f6d7bb..0fea816d9946 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -5226,7 +5226,6 @@ static int evict_folios(struct lruvec *lruvec, struct scan_control *sc, int swap
/* 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);