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[PATCH] debugobjects: Make kmemleak ignore debug objects

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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>
---
 init/main.c        | 2 +-
 lib/debugobjects.c | 3 +++
 2 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/init/main.c b/init/main.c
index 59d197e..8828fc1 100644
--- a/init/main.c
+++ b/init/main.c
@@ -660,8 +660,8 @@ 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)
diff --git a/lib/debugobjects.c b/lib/debugobjects.c
index 17afb04..2f5349c 100644
--- a/lib/debugobjects.c
+++ b/lib/debugobjects.c
@@ -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);
 	}
 
-- 
1.8.3.1

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[PATCH] debugobjects: Make kmemleak ignore debug objects Waiman Long <longman@redhat.com> - 2017-08-14 16:00 +0200
  [tip:core/debugobjects] debugobjects: Make kmemleak ignore debug  objects tip-bot for Waiman Long <tipbot@zytor.com> - 2017-08-14 17:00 +0200

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