linux-kernel - Re: [GIT pull] futex fixes for 2.6.31

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Message-ID: <20090625100413.GD29980@elte.hu>
Date:	Thu, 25 Jun 2009 12:04:13 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Darren Hart <dvhltc@...ibm.com>
Subject: Re: [GIT pull] futex fixes for 2.6.31


* Thomas Gleixner <tglx@...utronix.de> wrote:

> On Thu, 25 Jun 2009, Zhang, Yanmin wrote:
> > On Wed, 2009-06-24 at 21:48 +0200, Thomas Gleixner wrote:
> > > +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?
> 
> Grrr. I looked up the prototype of it in include/linux/mm.h:
> 
> int get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
> 			unsigned long start, int len, int write, int force,
> 			struct page **pages, struct vm_area_struct **vmas);
> 
> len == number of pages ! How intutitive. :(
> 
> I guess Linus tripped over it as well. See:
> http://lkml.org/lkml/2009/6/21/95

heh, and then i suggested to you to change the '4' to sizeof(u32) 
;-)

	Ingo
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