Slab memory leak in JFFS2 filesystems

[Johns Daniel]

On Fri, Feb 25, 2011 at 10:27 AM, Artem Bityutskiy <dedekind1 at gmail.com> wrote:
> On Fri, 2011-02-25 at 10:12 -0600, Johns Daniel wrote:
>> On Fri, Feb 25, 2011 at 6:38 AM, Artem Bityutskiy <dedekind1 at gmail.com> wrote:
>> > On Thu, 2011-02-24 at 18:41 -0600, Johns Daniel wrote:
>> >> I have discovered a kernel memory leak associated with JFFS2
>> >> filesystems. I have verified the leak in kernels 2.6.28 and 2.6.36 on
>> >> a Freescale PowerPC board using this script:
>> >>
>> >> while :; do FN=$(mktemp /jffs2fs/TMP.XXXXXXXX); \
>> >>    cat /proc/slabinfo |grep "dentry\|size-64 "; sleep 1; /bin/rm $FN; done
>> >
>> > Please, check whether they go away after:
>> >
>> > echo 3 > /proc/sys/vm/drop_caches
>> >
>> > See Documentation/sysctl/vm.txt for more information about what this
>> > means.
>>
>> Thanks for that suggestion, Artem! Here is what I tried:
>
> Hi, you can try to play with kmemleak - this is a kernel feature which
> slows down the system a lot but is great in catching memory leaks. It
> may have false positives sometimes, though. You can read about kmemleak
> in the Documentation/ directory. I think if there are leaks in JFFS2 -
> kmemleak would spot them.
>

Unfortunately, the kmemleak feature is not supported on PPC even in
2.6.36. And I don't have a supported system available with the JFFS2
filesystem.

One more data point. After running the script like this:

while :; do FN=$(mktemp /jffs2fs/TMP.XXXXXXXX); \
   echo 3 > /proc/sys/vm/drop_caches; sleep 1; \
   grep  "dentry\|size-64 " /proc/slabinfo; /bin/rm $FN; done

it looks like the leak may only be in "size-64" (and not "dentry").

> --
> Best Regards,
> Artem Bityutskiy (Битюцкий Артём)
>
>