Commit caba4cbb authored Aug 14, 2017 by Waiman Long Committed by Thomas Gleixner Aug 14, 2017

debugobjects: Make kmemleak ignore debug objects



The allocated debug objects are either on the free list or in the
hashed bucket lists. So they won't get lost. However if both debug
objects and kmemleak are enabled and kmemleak scanning is done
while some of the debug objects are transitioning from one list to
the others, false negative reporting of memory leaks may happen for
those objects. For example,

[38687.275678] kmemleak: 12 new suspected memory leaks (see
/sys/kernel/debug/kmemleak)
unreferenced object 0xffff92e98aabeb68 (size 40):
  comm "ksmtuned", pid 4344, jiffies 4298403600 (age 906.430s)
  hex dump (first 32 bytes):
    00 00 00 00 00 00 00 00 d0 bc db 92 e9 92 ff ff  ................
    01 00 00 00 00 00 00 00 38 36 8a 61 e9 92 ff ff  ........86.a....
  backtrace:
    [<ffffffff8fa5378a>] kmemleak_alloc+0x4a/0xa0
    [<ffffffff8f47c019>] kmem_cache_alloc+0xe9/0x320
    [<ffffffff8f62ed96>] __debug_object_init+0x3e6/0x400
    [<ffffffff8f62ef01>] debug_object_activate+0x131/0x210
    [<ffffffff8f330d9f>] __call_rcu+0x3f/0x400
    [<ffffffff8f33117d>] call_rcu_sched+0x1d/0x20
    [<ffffffff8f4a183c>] put_object+0x2c/0x40
    [<ffffffff8f4a188c>] __delete_object+0x3c/0x50
    [<ffffffff8f4a18bd>] delete_object_full+0x1d/0x20
    [<ffffffff8fa535c2>] kmemleak_free+0x32/0x80
    [<ffffffff8f47af07>] kmem_cache_free+0x77/0x350
    [<ffffffff8f453912>] unlink_anon_vmas+0x82/0x1e0
    [<ffffffff8f440341>] free_pgtables+0xa1/0x110
    [<ffffffff8f44af91>] exit_mmap+0xc1/0x170
    [<ffffffff8f29db60>] mmput+0x80/0x150
    [<ffffffff8f2a7609>] do_exit+0x2a9/0xd20

The references in the debug objects may also hide a real memory leak.

As there is no point in having kmemleak to track debug object
allocations, kmemleak checking is now disabled for debug objects.

Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Link: http://lkml.kernel.org/r/1502718733-8527-1-git-send-email-longman@redhat.com

parent ef954844

init/main.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -651,8 +651,8 @@ asmlinkage __visible void __init start_kernel(void)
		}
		#endif
		page_ext_init();
		debug_objects_mem_init();
		kmemleak_init();
		debug_objects_mem_init();
		setup_per_cpu_pageset();
		numa_policy_init();
		if (late_time_init)

lib/debugobjects.c

+3 −0

Original line number	Diff line number	Diff line
		@@ -18,6 +18,7 @@
		#include <linux/debugfs.h>
		#include <linux/slab.h>
		#include <linux/hash.h>
		#include <linux/kmemleak.h>

		#define ODEBUG_HASH_BITS 14
		#define ODEBUG_HASH_SIZE (1 << ODEBUG_HASH_BITS)
		@@ -110,6 +111,7 @@ static void fill_pool(void)
		if (!new)
		return;

		kmemleak_ignore(new);
		raw_spin_lock_irqsave(&pool_lock, flags);
		hlist_add_head(&new->node, &obj_pool);
		debug_objects_allocated++;
		@@ -1080,6 +1082,7 @@ static int __init debug_objects_replace_static_objects(void)
		obj = kmem_cache_zalloc(obj_cache, GFP_KERNEL);
		if (!obj)
		goto free;
		kmemleak_ignore(obj);
		hlist_add_head(&obj->node, &objects);
		}

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