Re: [RFC]: Possible race condition in kernel futex code

From	Peter Zijlstra <peterz@infradead.org>
Newsgroups	linux.kernel
Subject	Re: [RFC]: Possible race condition in kernel futex code
Date	2015-10-09 13:40 +0200
Message-ID	<qhEbN-R9-25@gated-at.bofh.it> (permalink)
References	<qgfSa-2Pr-33@gated-at.bofh.it> <qhBQC-63L-23@gated-at.bofh.it> <qhCCZ-6Yo-3@gated-at.bofh.it> <qhD61-7Lm-5@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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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.
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Thread

Re: [RFC]: Possible race condition in kernel futex code Thomas Gleixner <tglx@linutronix.de> - 2015-10-09 11:10 +0200
  Re: [RFC]: Possible race condition in kernel futex code Hans Zuidam <h.zuidam@online.nl> - 2015-10-09 12:00 +0200
    Re: [RFC]: Possible race condition in kernel futex code Thomas Gleixner <tglx@linutronix.de> - 2015-10-09 12:30 +0200
      Re: [RFC]: Possible race condition in kernel futex code Peter Zijlstra <peterz@infradead.org> - 2015-10-09 13:40 +0200
  Re: [RFC]: Possible race condition in kernel futex code Greg KH <greg@kroah.com> - 2015-10-18 02:30 +0200

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