Re: Gigantic memory leak in linux-2.6.[789]!

["Kristian Sørensen" <ks@cs.aau.dk>]

Richard B. Johnson wrote:

> On Fri, 22 Oct 2004, [ISO-8859-15] Kristian Sørensen wrote:
>
>> Richard B. Johnson wrote:
>>
>>> On Fri, 22 Oct 2004, Kasper Sandberg wrote:
>>>
>>>> On Fri, 2004-10-22 at 16:13 +0200, Kristian Sørensen wrote:
>>>>
>>>>> Hi all!
>>>>>
>>>>> After some more testing after the previous post of the OOPS in
>>>>> generic_delete_inode, we have now found a gigantic memory leak in 
>>>>> Linux 2.6.
>>>>> [789]. The scenario is the same:
>>>>>
>>>>> File system: EXT3
>>>>> Unpack and delete linux-2.6.8.1.tar.bz2 with this Bash while loop:
>>>>>
>>>>> let "i = 0"
>>>>> while [ "$i" -lt 10 ]; do
>>>>>    tar jxf linux-2.6.8.1.tar.bz2;
>>>>>    rm -fr linux-2.6.8.1;
>>>>>    let "i = i + 1"
>>>>> done
>>>>>
>>>>> When the loop has completed, the system use 124 MB memory more 
>>>>> _each_ time....
>>>>> so it is pretty easy to make a denial-of-service attack :-(
>>>>
>>>
>>>
>>>
>>> Do something like this with your favorite kernel version.....
>>>
>>> while true ; do tar -xzf linux-2.6.9.tar.gz ; rm -rf linux-2.6.9 ; 
>>> vmstat ; done
>>>
>>> You can watch this for as long as you want. If there is no other
>>> activity, the values reported by vmstat remain, on the average, stable.
>>> If you throw in a `sync` command, the values rapidly converge to
>>> little memory usage as the disk-data gets flused to disk.
>>
>> The problem is, that the free memory reported by vmstat is decresing 
>> by 124mb for each 10-iterations....
>>
>> The allocated memory does not get freed even if the system has been 
>> left alone for three hours!
>>
>
> Yes. So?  Why would it be freed? It's left how it was until it
> is needed. Freeing it would waste CPU cycles.

Okay :-) So it looks like two of you says we have been mistaken :-D (and 
the behaviour has been changed since linux-2.4)

Anyway - How does this work in practice? Does the file system 
implementation use a wrapper for kfree or?
Is there any way to force instant free of kernel memory - when freed? 
Else it is quite hard testing for possible memory leaks in our Umbrella 
kernel module ... :-/


Best regards,

-- 
Kristian Sørensen
- The Umbrella Project
  http://umbrella.sourceforge.net

E-mail: ipqw@users.sf.net, Phone: +45 29723816