Message-ID: <484BC4DF.5000605@thorsten-knabe.de>
Date: Sun, 08 Jun 2008 13:39:11 +0200
From: Thorsten Knabe <linux@thorsten-knabe.de>
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To: Jeff Dike <jdike@addtoit.com>
CC: Chris Wright <chrisw@sous-sol.org>, linux-kernel@vger.kernel.org
Subject: Re: [BUG] Linux 2.6.25.4 task_struct leak
References: <483EC624.90503@thorsten-knabe.de> <20080601213134.GJ4018@sequoia.sous-sol.org> <20080602010546.GA8578@c2.user-mode-linux.org> <484719C7.2020502@thorsten-knabe.de> <20080605004925.GA15461@c2.user-mode-linux.org>
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Jeff Dike wrote:
> I misunderstood - I thought you were seeing a task_struct leak within
> UML rather than a leak on the host elicited by UML.
> 
>> As far as I understand the UML code in the kernel, an UML kernel uses
>> some unusual clone() flags when creating new processes, which are seldom
>> used by other applications and could be related to the bug.
> 
> Yes, it does.  I don't see the flags causing a leak, though.  What
> might be more likely (although I really have no idea) is ptrace.
> Possibly a reference is held when it should have been dropped.  This
> might also show up with strace or gdb.

Hello Jeff.

Your assumption about ptrace causing the task_struct leak seems to be
right. I bisected the problem down to a few commits using the repository
at git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6.git.

Commit b7b71725fb9584454bfe5f231223bd63421798fb is the last known commit
that does not leak task_structs, whereas commit
a97f52e67890fda6b373c1c1895ff1c1c69b36c8 is leaking task_structs.
Revisions in between do not even compile.
Also I had to apply the changes from commit
f9cb02b0be4de3c51edfdd701754e13d9a2d20d6 to most of the kernels I have
tested, otherwise the UML process would crash on startup.

HTH
Thorsten

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