[PATCH v2 1/3] 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.

CONFIG_DEBUG_KMEMLEAK_VERBOSE depends on CONFIG_DEBUG_KMEMLEAK_AUTO_SCAN,
so a kernel built with it runs the scan thread periodically and the user
has opted into detailed leak reporting. A second confirming scan then
happens on its own.

Default min_unref_scans to 2 there to suppress transient false positives,
and keep it at 1 otherwise, where a manually triggered scan is expected to
report immediately. The value stays writable through the module parameter.

CONFIG_DEBUG_KMEMLEAK_VERBOSE defaults to n, so this does not change the
default for kernels that do not opt in.

Signed-off-by: Breno Leitao <leitao@xxxxxxxxxx>
---
 mm/kmemleak.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/mm/kmemleak.c b/mm/kmemleak.c
index f63dfacee7ca1..8fa409a4f9fb2 100644
--- a/mm/kmemleak.c
+++ b/mm/kmemleak.c
@@ -237,7 +237,8 @@ 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;
+static unsigned int min_unref_scans =
+	IS_ENABLED(CONFIG_DEBUG_KMEMLEAK_VERBOSE) ? 2 : 1;
 module_param(min_unref_scans, uint, 0644);
 static unsigned long jiffies_last_scan;
 /* delay between automatic memory scannings */

-- 
2.53.0-Meta