From 4f93f0956f446e270222c58f821de7500a163229 Mon Sep 17 00:00:00 2001 From: Youngjun Park Date: Mon, 13 Jul 2026 13:50:14 +0900 Subject: [PATCH] mm/swap: clarify unreachable cond_resched() in swap_reclaim_full_clusters Commit 66366d291f66 ("mm/swap: add cond_resched() in swap_reclaim_full_clusters to prevent softlockup") added cond_resched() to prevent soft lockups during heavy swap reclaim. Currently, there are two call sites for this function: 1. swap_reclaim_work(): called with force=true in a workqueue context. 2. cluster_alloc_swap_entry(): called with force=false, holding a local_lock and potentially a global cluster spinlock (atomic context). In the second case, calling cond_resched() would normally cause a "scheduling while atomic" bug. However, it is currently safe because when force=false, 'to_scan' is initialized to 1. The loop decrements it to 0 and breaks before ever reaching cond_resched(). This implicit dependency is hard to notice and recently triggered a false positive in AI Sashiko review. Add a comment to explicitly clarify that cond_resched() is unreachable in atomic contexts. This improves readability and prevents future misuse if the loop logic or 'to_scan' initialization is modified. Link: https://sashiko.dev/#/patchset/20260713025644.170839-1-youngjun.park@lge.com?part=4 Link: https://lore.kernel.org/20260713045014.219653-1-youngjun.park@lge.com Signed-off-by: Youngjun Park Cc: Baoquan He Cc: Barry Song Cc: Chris Li Cc: Kairui Song Cc: Kemeng Shi Cc: Nhat Pham Signed-off-by: Andrew Morton --- mm/swapfile.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/mm/swapfile.c b/mm/swapfile.c index 775c385490a5..095d43838d4e 100644 --- a/mm/swapfile.c +++ b/mm/swapfile.c @@ -1072,6 +1072,12 @@ static void swap_reclaim_full_clusters(struct swap_info_struct *si, bool force) swap_cluster_unlock(ci); if (to_scan <= 0) break; + + /* + * When 'force' is false, 'to_scan' is initialized to 1. + * The loop breaks above, making this cond_resched() unreachable + * in atomic contexts. + */ cond_resched(); } }