linux-kernel - Re: [PATCH] futex: cmpxchg_futex_value

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Message-ID: <20110311021654.GA26122@google.com>
Date:	Thu, 10 Mar 2011 18:16:54 -0800
From:	Michel Lespinasse <walken@...gle.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Darren Hart <darren@...art.com>, Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <peterz@...radead.org>,
	Matt Turner <mattst88@...il.com>,
	Russell King <linux@....linux.org.uk>,
	David Howells <dhowells@...hat.com>,
	Tony Luck <tony.luck@...el.com>,
	Michal Simek <monstr@...str.eu>,
	Ralf Baechle <ralf@...ux-mips.org>,
	"James E.J. Bottomley" <jejb@...isc-linux.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Paul Mundt <lethal@...ux-sh.org>,
	"David S. Miller" <davem@...emloft.net>,
	Chris Metcalf <cmetcalf@...era.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] futex: cmpxchg_futex_value_locked API change

On Thu, Mar 10, 2011 at 07:55:05PM +0100, Thomas Gleixner wrote:
> On Wed, 9 Mar 2011, Michel Lespinasse wrote:
> > On Tue, Mar 08, 2011 at 09:17:11PM +0100, Thomas Gleixner wrote:
> 
> Just looked at it again in detail before picking it up. Can we please
> separate the s/int/u32/ changes from the real API change ?
> 
> > -	pagefault_disable();	/* implies preempt_disable() */
> > +	/* Note that preemption is disabled by futex_atomic_cmpxchg_inatomic
> > +	 * call sites. */
> 
> That wants to be a separate patch as well.

No problems. That makes it 3 patches, will send as replies to this.

> > -int futex_atomic_op_inuser(int encoded_op, int __user *uaddr)
> > +int futex_atomic_op_inuser(int encoded_op, u32 __user *uaddr)
> >  {
> >  	int op = (encoded_op >> 28) & 7;
> >  	int cmp = (encoded_op >> 24) & 15;
> > @@ -197,7 +197,7 @@ int futex_atomic_op_inuser(int encoded_op, int __user *uaddr)
> >  	if (encoded_op & (FUTEX_OP_OPARG_SHIFT << 28))
> >  		oparg = 1 << oparg;
> >  
> > -	if (!access_ok(VERIFY_WRITE, uaddr, sizeof(int)))
> > +	if (!access_ok(VERIFY_WRITE, uaddr, sizeof(u32)))
> >  		return -EFAULT;
> >  
> >  	pagefault_disable();
> 
> So following the reasoning above, shouldn't that be the same for
> futex_atomic_op_inuser() ?

futex_atomic_op_inuser() is currently called by core futex code with
page faults enabled. I think that's OK - for futex_atomic_cmpxchg_inatomic
I fixed the arm implementation because it was inconsistent with the
other ones, but for futex_atomic_op_inuser() every arch does it
that way.

-- 
Michel "Walken" Lespinasse
A program is never fully debugged until the last user dies.
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