[PATCH] mm: kmemleak: default min_unref_scans to 2 for verbose auto-scan

[PATCH] mm: kmemleak: default min_unref_scans to 2 for verbose auto-scan

[Breno Leitao]

min_unref_scans defers reporting an object as leaked until it has stayed
unreferenced for that many consecutive scans, filtering out objects that
are only transiently unreferenced during a scan.

It defaults to 1, which reports on the first unreferenced scan.

When CONFIG_DEBUG_KMEMLEAK_AUTO_SCAN and CONFIG_DEBUG_KMEMLEAK_VERBOSE are
both enabled, the scan thread runs periodically and the user has opted into
detailed leak reporting, so a second confirming scan happens on its own.

Default min_unref_scans to 2 in that configuration to suppress transient
false positives.

Keep the default at 1 otherwise, where a manually triggered scan is
expected to report immediately. The value stays writable through the module
parameter.

Signed-off-by: Breno Leitao <leitao@debian.org>
---
 mm/kmemleak.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/mm/kmemleak.c b/mm/kmemleak.c
index f63dfacee7ca1..6c31e66915ec7 100644
--- a/mm/kmemleak.c
+++ b/mm/kmemleak.c
@@ -237,7 +237,13 @@ static struct task_struct *scan_thread;
 /* used to avoid reporting of recently allocated objects */
 static unsigned long jiffies_min_age;
 /* consecutive scans an object must stay unreferenced before reporting */
-static unsigned int min_unref_scans = 1;
+#if IS_ENABLED(CONFIG_DEBUG_KMEMLEAK_VERBOSE) && \
+	IS_ENABLED(CONFIG_DEBUG_KMEMLEAK_AUTO_SCAN)
+#define MIN_UNREF_SCANS_DEFAULT	2
+#else
+#define MIN_UNREF_SCANS_DEFAULT	1
+#endif
+static unsigned int min_unref_scans = MIN_UNREF_SCANS_DEFAULT;
 module_param(min_unref_scans, uint, 0644);
 static unsigned long jiffies_last_scan;
 /* delay between automatic memory scannings */

---
base-commit: 78bc8af4affb9a732504eb22eeac7d1e50883853
change-id: 20260730-kmemleak_hardened-e80542d1152f

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

Re: [PATCH] mm: kmemleak: default min_unref_scans to 2 for verbose auto-scan

[Catalin Marinas]

On Thu, Jul 30, 2026 at 07:31:21AM -0700, Breno Leitao wrote:
> min_unref_scans defers reporting an object as leaked until it has stayed
> unreferenced for that many consecutive scans, filtering out objects that
> are only transiently unreferenced during a scan.
> 
> It defaults to 1, which reports on the first unreferenced scan.
> 
> When CONFIG_DEBUG_KMEMLEAK_AUTO_SCAN and CONFIG_DEBUG_KMEMLEAK_VERBOSE are
> both enabled, the scan thread runs periodically and the user has opted into
> detailed leak reporting, so a second confirming scan happens on its own.
> 
> Default min_unref_scans to 2 in that configuration to suppress transient
> false positives.
> 
> Keep the default at 1 otherwise, where a manually triggered scan is
> expected to report immediately. The value stays writable through the module
> parameter.
> 
> Signed-off-by: Breno Leitao <leitao@debian.org>

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

Re: [PATCH] mm: kmemleak: default min_unref_scans to 2 for verbose auto-scan

[Catalin Marinas]

On Mon, Aug 03, 2026 at 02:41:20PM +0100, Catalin Marinas wrote:
> On Thu, Jul 30, 2026 at 07:31:21AM -0700, Breno Leitao wrote:
> > min_unref_scans defers reporting an object as leaked until it has stayed
> > unreferenced for that many consecutive scans, filtering out objects that
> > are only transiently unreferenced during a scan.
> > 
> > It defaults to 1, which reports on the first unreferenced scan.
> > 
> > When CONFIG_DEBUG_KMEMLEAK_AUTO_SCAN and CONFIG_DEBUG_KMEMLEAK_VERBOSE are
> > both enabled, the scan thread runs periodically and the user has opted into
> > detailed leak reporting, so a second confirming scan happens on its own.
> > 
> > Default min_unref_scans to 2 in that configuration to suppress transient
> > false positives.
> > 
> > Keep the default at 1 otherwise, where a manually triggered scan is
> > expected to report immediately. The value stays writable through the module
> > parameter.
> > 
> > Signed-off-by: Breno Leitao <leitao@debian.org>
> 
> Acked-by: Catalin Marinas <catalin.marinas@arm.com>

Ah, I noticed there's a v2. Ignore this one.

-- 
Catalin