linux-kernel - Re: futex question

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Date:	Mon, 5 Oct 2009 13:47:39 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
cc:	Anirban Sinha <ani@...rban.org>, Ingo Molnar <mingo@...e.hu>,
	linux-kernel@...r.kernel.org, Darren Hart <dvhltc@...ibm.com>,
	Kaz Kylheku <kaz@...gmasystems.com>,
	Anirban Sinha <asinha@...gmasystems.com>
Subject: Re: futex question

On Mon, 5 Oct 2009, Peter Zijlstra wrote:
> On Mon, 2009-10-05 at 12:56 +0200, Thomas Gleixner wrote:
> > 
> > Looking more into that I think we should check whether the robust list
> > has an entry (lock held) in do_execve() and return -EWOULDBLOCK to
> > luser space. Same if pi_waiters is not empty. Holding a lock and
> > calling execve() is simply broken.
> 
> Fine by me ;-)
> 
> something like the below?
> 
> The question is of course what Ani was doing that triggered this in the
> first place and if he can live with this.. :-)
> 
> ---
>  fs/exec.c |   16 ++++++++++++++++
>  1 files changed, 16 insertions(+), 0 deletions(-)
> 
> diff --git a/fs/exec.c b/fs/exec.c
> index d49be6b..0812ba6 100644
> --- a/fs/exec.c
> +++ b/fs/exec.c
> @@ -1295,6 +1295,22 @@ int do_execve(char * filename,
>  	bool clear_in_exec;
>  	int retval;
>  
> +	retval = -EWOULDBLOCK;
> +#ifdef CONFIG_FUTEX
> +	if (unlikely(current->robust_list))
> +		goto out_ret;
> +#ifdef CONFIG_COMPAT
> +	if (unlikely(current->compat_robust_list))
> +		goto out_ret;
> +#endif

  That needs to call into the futex code and check whether the list is
  empty. If not empty, return. If empty set the pointer to NULL

Thanks,

	tglx
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