From dd0dcfe8ef21fb73dbc48af5c630ef2a6f4ab27c Mon Sep 17 00:00:00 2001 From: Breno Leitao Date: Fri, 31 Jul 2026 03:13:04 -0700 Subject: [PATCH] mm: kmemleak: default min_unref_scans to 2 for verbose auto-scan Patch series "mm: kmemleak: default min_unref_scans to 2 for verbose kernels", v2. When CONFIG_DEBUG_KMEMLEAK_VERBOSE is set, which means the host is in auto scan mode, set min_unref_scans to 2, avoiding false positives. CONFIG_DEBUG_KMEMLEAK_VERBOSE depends on CONFIG_DEBUG_KMEMLEAK_AUTO_SCAN, so a kernel built with it already runs the scan thread periodically and the user has asked for detailed leak reports. The confirming second scan comes for free there, so default min_unref_scans to 2 in that case and keep it at 1 everywhere else. CONFIG_DEBUG_KMEMLEAK_VERBOSE defaults to n, so nothing changes for kernels that do not opt in. The other two patches bring the documentation and the selftest comments in line with the new conditional default. PS: A similar patch (v1 of this patchset) is applied to Meta's kernel, in real production hosts. This patch (of 3): 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. Link: https://lore.kernel.org/20260731-kmemleak_hardened-v2-0-7b9689ac77cb@debian.org Link: https://lore.kernel.org/20260731-kmemleak_hardened-v2-1-7b9689ac77cb@debian.org Signed-off-by: Breno Leitao Acked-by: Catalin Marinas Cc: David Hildenbrand Cc: Jonathan Corbet Cc: Liam R. Howlett Cc: Lorenzo Stoakes Cc: Michal Hocko Cc: Mike Rapoport Cc: Shuah Khan Cc: Suren Baghdasaryan Cc: Vlastimil Babka Signed-off-by: Andrew Morton --- mm/kmemleak.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/mm/kmemleak.c b/mm/kmemleak.c index f63dfacee7ca..8fa409a4f9fb 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 */