From: Peter Zijlstra <peterz@infradead.org>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Hans Zuidam <h.zuidam@computer.org>,
Jaccon Bastiaansen <jaccon.bastiaansen@gmail.com>,
x86@kernel.org, mingo@redhat.com,
"H. Peter Anvin" <hpa@zytor.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
stable@vger.kernel.org,
Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [RFC]: Possible race condition in kernel futex code
Date: Fri, 9 Oct 2015 13:35:52 +0200 [thread overview]
Message-ID: <20151009113552.GC3816@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <alpine.DEB.2.11.1510091054230.6097@nanos>
On Fri, Oct 09, 2015 at 11:25:09AM +0100, Thomas Gleixner wrote:
> Hans,
>
> On Fri, 9 Oct 2015, Hans Zuidam wrote:
> > On 9 okt. 2015, at 11:06, Thomas Gleixner <tglx@linutronix.de> wrote:
> > > You cannot use an explicit 32bit read. We need an access which
> > > handles the fault gracefully.
> >
> > The reason for the explicit read suggestion is to avoid the
> > _builtin_constant_p() in __copy_from_user_nocheck(). The GCC manual
> > says that there may be situations where it returns 0 even though the
> > argument is a constant.
>
> That's insane at best.
Right, but I bet that is for cases where constant propagation completely
fails, and this is a trivial case, I have no problem relying on it.
next prev parent reply other threads:[~2015-10-09 11:36 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-10-05 15:11 [RFC]: Possible race condition in kernel futex code Jaccon Bastiaansen
2015-10-09 9:06 ` Thomas Gleixner
2015-10-09 9:49 ` Hans Zuidam
2015-10-09 10:25 ` Thomas Gleixner
2015-10-09 11:35 ` Peter Zijlstra [this message]
2015-10-18 0:23 ` Greg KH
2016-05-15 22:34 ` Ben Hutchings
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