[PATCH] mm/kmemleak: skip the remaining scan phases when interrupted

[PATCH] mm/kmemleak: skip the remaining scan phases when interrupted

[Breno Leitao]

kmemleak_scan() scans the per-cpu sections, the struct page ranges and
the task stacks in sequence. Each loop now bails out once scan_block()
reports the scan was interrupted, but the later phases are still entered
and only bail on their first scan_block() call.

Jump straight to the gray list scan once a phase reports an interrupted
scan, so the remaining scan phases are not entered at all. This does not
change the scan results, it only avoids the pointless re-entry.

Suggested-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Breno Leitao <leitao@debian.org>
---
 mm/kmemleak.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/mm/kmemleak.c b/mm/kmemleak.c
index 7fa7124727e36..68a0e30eea1e3 100644
--- a/mm/kmemleak.c
+++ b/mm/kmemleak.c
@@ -1850,6 +1850,7 @@ static void kmemleak_scan(void)
 	int __maybe_unused i;
 	struct xarray dedup;
 	int new_leaks = 0;
+	int stop = 0;
 
 	jiffies_last_scan = jiffies;
 
@@ -1896,7 +1897,7 @@ static void kmemleak_scan(void)
 	for_each_possible_cpu(i) {
 		if (scan_large_block(__per_cpu_start + per_cpu_offset(i),
 				     __per_cpu_end + per_cpu_offset(i)))
-			break;
+			goto scan_gray;
 	}
 #endif
 
@@ -1908,7 +1909,6 @@ static void kmemleak_scan(void)
 		unsigned long start_pfn = zone->zone_start_pfn;
 		unsigned long end_pfn = zone_end_pfn(zone);
 		unsigned long pfn;
-		int stop = 0;
 
 		for (pfn = start_pfn; pfn < end_pfn; pfn++) {
 			struct page *page = pfn_to_online_page(pfn);
@@ -1933,6 +1933,8 @@ static void kmemleak_scan(void)
 			break;
 	}
 	put_online_mems();
+	if (stop)
+		goto scan_gray;
 
 	/*
 	 * Scanning the task stacks (may introduce false negatives).
@@ -1944,6 +1946,7 @@ static void kmemleak_scan(void)
 	 * Scan the objects already referenced from the sections scanned
 	 * above.
 	 */
+scan_gray:
 	scan_gray_list();
 
 	/*

---
base-commit: 338a2c2582c8eddbc11cf35463a14a36c051afb5
change-id: 20260626-kmemleak_improve-944f76e04da9

Best regards,
-- 
Breno Leitao <leitao@debian.org>

Re: [PATCH] mm/kmemleak: skip the remaining scan phases when interrupted

[Catalin Marinas]

On Fri, Jun 26, 2026 at 10:56:23AM -0700, Breno Leitao wrote:
> kmemleak_scan() scans the per-cpu sections, the struct page ranges and
> the task stacks in sequence. Each loop now bails out once scan_block()
> reports the scan was interrupted, but the later phases are still entered
> and only bail on their first scan_block() call.
> 
> Jump straight to the gray list scan once a phase reports an interrupted
> scan, so the remaining scan phases are not entered at all. This does not
> change the scan results, it only avoids the pointless re-entry.
> 
> Suggested-by: Oleg Nesterov <oleg@redhat.com>
> Signed-off-by: Breno Leitao <leitao@debian.org>

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>