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Subject: Re: [GIT pull] futex fixes for 2.6.31
From: "Zhang, Yanmin" <yanmin_zhang@linux.intel.com>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
       LKML <linux-kernel@vger.kernel.org>, Ingo Molnar <mingo@elte.hu>,
       Peter Zijlstra <peterz@infradead.org>, Darren Hart <dvhltc@us.ibm.com>
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Date: Thu, 25 Jun 2009 10:43:46 +0800
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On Wed, 2009-06-24 at 21:48 +0200, Thomas Gleixner wrote:
> Linus,
> 
> Please pull the latest futexes-for-linus git tree from:
> 
>    git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip.git futexes-for-linus
> 
> Thanks,
> 
> 	tglx
> 
> ------------------>
> Thomas Gleixner (1):
>       futex: Fix the write access fault problem for real
> 
> 
>  kernel/futex.c |   45 ++++++++++++++++++++++++---------------------
>  1 files changed, 24 insertions(+), 21 deletions(-)
> 
> diff --git a/kernel/futex.c b/kernel/futex.c
> index 80b5ce7..1c33711 100644
> --- a/kernel/futex.c
> +++ b/kernel/futex.c
> @@ -284,6 +284,25 @@ void put_futex_key(int fshared, union futex_key *key)
>  	drop_futex_key_refs(key);
>  }
>  
> +/*
> + * fault_in_user_writeable - fault in user address and verify RW access
> + * @uaddr:	pointer to faulting user space address
> + *
> + * Slow path to fixup the fault we just took in the atomic write
> + * access to @uaddr.
> + *
> + * We have no generic implementation of a non destructive write to the
> + * user address. We know that we faulted in the atomic pagefault
> + * disabled section so we can as well avoid the #PF overhead by
> + * calling get_user_pages() right away.
> + */
> +static int fault_in_user_writeable(u32 __user *uaddr)
> +{
> +	int ret = get_user_pages(current, current->mm, (unsigned long)uaddr,
> +				 sizeof(*uaddr), 1, 0, NULL, NULL);
The 4th parameter of get_user_pages means page number. sizeof(*uaddr) is equal to
4, so you want 4 pages?

Yanmin