linux-kernel - Re: [PATCH v2] fork: fix oops after fork failure

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Message-Id: <20120824150804.8e3c4b7e.akpm@linux-foundation.org>
Date:	Fri, 24 Aug 2012 15:08:04 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Glauber Costa <glommer@...allels.com>
Cc:	<linux-kernel@...r.kernel.org>, <torvalds@...ux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Tony Luck <tony.luck@...el.com>,
	Fenghua Yu <fenghua.yu@...el.com>
Subject: Re: [PATCH v2] fork: fix oops after fork failure

On Thu, 23 Aug 2012 19:36:08 +0400
Glauber Costa <glommer@...allels.com> wrote:

> When we want to duplicate a new process, dup_task_struct() will undergo
> a series of allocations. If alloc_thread_info_node() fails, we call
> free_task_struct() and return.
> 
> This seems right, but it is not. free_task_struct() will not only free
> the task struct from the kmem_cache, but will also call
> arch_release_task_struct(). The problem is that this function is
> supposed to undo whatever arch-specific work done by
> arch_dup_task_struct(), that is not yet called at this point.  The
> particular problem I ran accross was that in x86, we will arrive at
> fpu_free() without having ever allocated it.

I think ths was already fixed by f19b9f74b7ea3b ("fork: fix error
handling in dup_task()").  As you would have noticed if you were
preparing patches against up-to-date kernel versions!

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