linux-kernel - [PATCH] mm/kmemleak: Move up cond_resched() call in page scanning loop

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Date:   Fri, 25 Aug 2023 12:49:47 -0400
From:   Waiman Long <longman@...hat.com>
To:     Catalin Marinas <catalin.marinas@....com>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Yisheng Xie <xieyisheng1@...wei.com>,
        Waiman Long <longman@...hat.com>
Subject: [PATCH] mm/kmemleak: Move up cond_resched() call in page scanning loop

Commit bde5f6bc68db ("kmemleak: add scheduling point to kmemleak_scan()")
added a cond_resched() call to the struct page scanning loop to prevent
soft lockup from happening. However, soft lockup can still happen in
that loop in some corner cases when the pages that satisfy the "!(pfn &
63)" check are skipped for some reasons.

Fix this corner case by moving up the cond_resched() check so that it
will be called every 64 pages unconditionally.

Fixes: bde5f6bc68db ("kmemleak: add scheduling point to kmemleak_scan()")
Signed-off-by: Waiman Long <longman@...hat.com>
---
 mm/kmemleak.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/mm/kmemleak.c b/mm/kmemleak.c
index a2d34226e3c8..114d8dcdcf70 100644
--- a/mm/kmemleak.c
+++ b/mm/kmemleak.c
@@ -1579,6 +1579,9 @@ static void kmemleak_scan(void)
 		for (pfn = start_pfn; pfn < end_pfn; pfn++) {
 			struct page *page = pfn_to_online_page(pfn);
 
+			if (!(pfn & 63))
+				cond_resched();
+
 			if (!page)
 				continue;
 
@@ -1589,8 +1592,6 @@ static void kmemleak_scan(void)
 			if (page_count(page) == 0)
 				continue;
 			scan_block(page, page + 1, NULL);
-			if (!(pfn & 63))
-				cond_resched();
 		}
 	}
 	put_online_mems();
-- 
2.31.1