Re: kmemleak false positive?

Dave Jones
2009-06-25T15:40:28Z

On Thu, Jun 25, 2009 at 04:25:39PM +0100, Catalin Marinas wrote:
> > Hmm, it's pretty noisy, and everything it's found so far looks to be
> > a false positive.
>
> In this case, it would make sense to enable task stacks scanning by
> default:
>
> diff --git a/mm/kmemleak.c b/mm/kmemleak.c
> index 17096d1..a38418a 100644
> --- a/mm/kmemleak.c
> +++ b/mm/kmemleak.c
> @@ -194,7 +194,7 @@ static unsigned long jiffies_min_age;
> /* delay between automatic memory scannings */
> static signed long jiffies_scan_wait;
> /* enables or disables the task stacks scanning */
> -static int kmemleak_stack_scan;
> +static int kmemleak_stack_scan = 1;

heh, I just did the same patch for the rawhide kernel builds.

> > > You can mount debugfs on /sys/kerne/debug and read the kmemleak file in
> > > there (it triggers a new scan as well).
> >
> > Currently prints the acpi traces I already posted.
>
> If they are still consistently shown with stack=on, it could be a leak.

Could be, though as you mentioned, with ACPI it's really hard to tell.

Here's another case (with stack scanning on btw) which looks odd..

kmemleak: unreferenced object 0xd86ba000 (size 16):
kmemleak: comm "init", pid 1, jiffies 4294683556
kmemleak: backtrace:
kmemleak: [<c04fd8b3>] kmemleak_alloc+0x193/0x2b8
kmemleak: [<c04f5e73>] kmem_cache_alloc+0x11e/0x174
kmemleak: [<c05cdfdc>] avtab_insertf+0xd6/0x140
kmemleak: [<c05ce3d7>] avtab_read_item+0x26a/0x284
kmemleak: [<c05ce5a5>] avtab_read+0x82/0xe5
kmemleak: [<c05d0618>] policydb_read+0x40c/0x1028
kmemleak: [<c05d459d>] security_load_policy+0x57/0x37c
kmemleak: [<c05c9995>] sel_write_load+0xb2/0x54a
kmemleak: [<c0500186>] vfs_write+0x9f/0x10f
kmemleak: [<c05002e1>] sys_write+0x58/0x8d
kmemleak: [<c040a8eb>] sysenter_do_call+0x12/0x38
kmemleak: [<ffffffff>] 0xffffffff

I looked over the SELinux code, and couldn't see an obvious leak.
Eric Paris came to the same conclusion.

Dave