+ mm-kmemleak-default-min_unref_scans-to-2-for-verbose-auto-scan.patch added to mm-new branch

The patch titled
     Subject: mm: kmemleak: default min_unref_scans to 2 for verbose auto-scan
has been added to the -mm mm-new branch.  Its filename is
     mm-kmemleak-default-min_unref_scans-to-2-for-verbose-auto-scan.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-kmemleak-default-min_unref_scans-to-2-for-verbose-auto-scan.patch

This patch will later appear in the mm-new branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Note, mm-new is a provisional staging ground for work-in-progress
patches, and acceptance into mm-new is a notification for others take
notice and to finish up reviews.  Please do not hesitate to respond to
review feedback and post updated versions to replace or incrementally
fixup patches in mm-new.

The mm-new branch of mm.git is not included in linux-next

If a few days of testing in mm-new is successful, the patch will me moved
into mm.git's mm-unstable branch, which is included in linux-next

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------------------------------------------------------
From: Breno Leitao <[email protected]>
Subject: mm: kmemleak: default min_unref_scans to 2 for verbose auto-scan
Date: Fri, 31 Jul 2026 03:13:04 -0700

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/[email protected]
Link: https://lore.kernel.org/[email protected]
Signed-off-by: Breno Leitao <[email protected]>
Acked-by: Catalin Marinas <[email protected]>
Cc: David Hildenbrand <[email protected]>
Cc: Jonathan Corbet <[email protected]>
Cc: Liam R. Howlett <[email protected]>
Cc: Lorenzo Stoakes <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Mike Rapoport <[email protected]>
Cc: Shuah Khan <[email protected]>
Cc: Suren Baghdasaryan <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
---

 mm/kmemleak.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/mm/kmemleak.c~mm-kmemleak-default-min_unref_scans-to-2-for-verbose-auto-scan
+++ a/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 */
_

Patches currently in -mm which might be from [email protected] are

mm-memory-failure-drop-dead-error_states-entry-for-reserved-pages.patch
mm-memory-failure-surface-unhandlable-kernel-pages-as-enotrecoverable.patch
mm-memory-failure-report-mf_msg_kernel-for-unrecoverable-kernel-pages.patch
mm-memory-failure-add-panic-option-for-unrecoverable-pages.patch
documentation-document-panic_on_unrecoverable_memory_failure-sysctl.patch
mm-kmemleak-report-leaks-only-after-n-consecutive-unreferenced-scans.patch
mm-kmemleak-factor-leak-confirmation-into-a-helper.patch
selftests-mm-test-kmemleaks-n-consecutive-scan-leak-confirmation.patch
mm-migrate-report-rcu-tasks-quiescent-states-in-migrate_pages_batch.patch
radix-tree-fix-kmemleak-false-positives-on-tree-head-reassignment.patch
mm-kmemleak-report-rcu-tasks-quiescent-states-during-the-scan.patch
mm-kmemleak-default-min_unref_scans-to-2-for-verbose-auto-scan.patch
documentation-kmemleak-document-the-conditional-min_unref_scans-default.patch
selftests-mm-kmemleak-drop-stale-min_unref_scans-default-from-comments.patch