netdev - Re: [Bugme-new] [Bug 10737] New: pktgen procfs problem

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Date:	Sun, 18 May 2008 17:31:01 +0200
From:	Patrick McHardy <kaber@...sh.net>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	netdev@...r.kernel.org, bugme-daemon@...zilla.kernel.org,
	devzero@....de, Robert Olsson <robert.olsson@....uu.se>,
	"Denis V. Lunev" <den@...nvz.org>,
	Pavel Emelyanov <xemul@...nvz.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Ben Greear <greearb@...delatech.com>
Subject: Re: [Bugme-new] [Bug 10737] New: pktgen procfs problem

Patrick McHardy wrote:
>>>> I've been looking into the same problem, without much success so
>>>> far. The problem appears to affect any /proc/net file, but not
>>>> files outside of /proc/net, so I'm guessing its net-ns related.
>>>> A testcase found by Ben Greear is opening the file multiple times:
>>>>
>>>> # /tmp/open /proc/net/kpktgen_0
>>>>
>>>> => refcnt goes to 1
>>>>
>>>> ^C
>>>>
>>>> => refcnt goes to 0
>>>>
>>>> Without ^C and opening the file a second time:
>>>>
>>>> # /tmp/open /proc/net/kpktgen_0
>>>>
>>>> => refcnt goes to 2 (sometimes also 11)
>>>>
>>>> ^C
>>>>
>>>> => refcnt stays at previous value.
>>>>
>>>> The refcnt even leaks if the file can't be successfully opened,
>>>> for example because of lacking permissions.
>>>>     
>>>
>>> urgh.  Is any of this known to be post-2.6.25?
>>>   
>>
>> 2.6.25 is also affected. I don't know about earlier kernels.
> 
> Some more information: the problem seems to occur only if
> the file is opened by two different processes.
> 
> I'm starting a bisection now.


git-bisect identified e9720acd ([NET]: Make /proc/net a symlink
on /proc/self/net (v3)) as the guilty commit. I couldn't find
the problem in that commit, so someone with a better understanding
of how this is supposed to work should look into it.


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