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Message-ID: <1402958985.15603.49.camel@rage>
Date: Mon, 16 Jun 2014 15:49:45 -0700
From: Darren Hart <darren@...art.com>
To: Thomas Gleixner <tglx@...utronix.de>
Cc: LKML <linux-kernel@...r.kernel.org>,
Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...nel.org>,
Davidlohr Bueso <davidlohr@...com>,
Kees Cook <kees@...flux.net>, wad@...omium.org
Subject: Re: [patch 1/5] futex: Make unlock_pi more robust
On Tue, 2014-06-17 at 00:28 +0200, Thomas Gleixner wrote:
> On Tue, 17 Jun 2014, Thomas Gleixner wrote:
> > On Mon, 16 Jun 2014, Darren Hart wrote:
> > > On Wed, 2014-06-11 at 20:45 +0000, Thomas Gleixner wrote:
> > > In wake_futex_pi we verify ownership by matching pi_state->owner ==
> > > current, but here the only test is the TID value, which is set by
> > > userspace - which we don't trust...
> > >
> > > I'm trying to determine if it matters in this case... if there are no
> > > waiters, is the pi_state still around? If so, it does indeed matter, and
> > > we should be verifying.
> >
> > Erm. The whole point of this patch is to do:
> >
> > - Find existing state first and handle it.
> >
> > - If no state exists and TID == current, take it
> >
> > - Otherwise create state
>
> Duh, that was the lock path. But here the point is:
>
> - Find existing state first and handle it.
>
> - If no state exists and TID == current, release it
>
Right, I understood your meaning, and I withdraw the concern.
> The retry is obvious, right?
Yes.
--
Darren Hart
Intel Open Source Technology Center
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