From: Thomas Gleixner <tglx@linutronix.de>
To: Darren Hart <darren@dvhart.com>
Cc: LKML <linux-kernel@vger.kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@kernel.org>,
Davidlohr Bueso <davidlohr@hp.com>, Kees Cook <kees@outflux.net>,
wad@chromium.org
Subject: Re: [patch V2 5/5] futex: Simplify futex_lock_pi_atomic() and make it more robust
Date: Tue, 17 Jun 2014 09:20:29 +0200 (CEST) [thread overview]
Message-ID: <alpine.DEB.2.10.1406170910010.5170@nanos> (raw)
In-Reply-To: <1402950997.15603.39.camel@rage>
On Mon, 16 Jun 2014, Darren Hart wrote:
> On Fri, 2014-06-13 at 11:44 +0200, Thomas Gleixner wrote:
> Two general concerns, we appear to be eliminating both the force_take
> and the retry.
>
> The force_take only occurs if TID==0, and that is covered here in a
> cleaner way, so I believe we are good here.
>
> As for the retry, the remaining use case (outside of TID==0 ->
> force_take=1 -> retry) appears to be that userspace changed the value
> while we were running. Reading the value early doesn't protect us from
> this scenario. How does this change account for that?
>
> It looks to me that before we would retry, while here we just give up
> and return -EAGAIN..., which is addressed in futex_lock_pi(), but not in
> the futex_requeue() callsite for futex_proxy_trylock_atomic. It does
> handle it, but I guess also needs a comment update to "The owner was
> exiting" to include "or userspace changed the value" as you did for
> futex_lock_pi().
Right. I moved the handling back to the call site which has to handle
the various error return codes anyway.
> >From my analysis, this is a good cleanup and makes the code for
> explicit. I'm nervous about missing corner cases, and would like to
> understand what level of testing this has received. We need to add PI
> locking tests to futextest. There are some in glibc. Which tests were
> run to validate PI locking?
I ran it against everything I have. libc tests, your stuff, rt-tests
and random exploit and corner case exposure code I collected/wrote in
the last few weeks.
Thanks,
tglx
next prev parent reply other threads:[~2014-06-17 7:20 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-06-11 20:45 [patch 0/5] futex: More robustness tweaks Thomas Gleixner
2014-06-11 20:45 ` [patch 1/5] futex: Make unlock_pi more robust Thomas Gleixner
2014-06-16 16:18 ` Darren Hart
2014-06-16 22:15 ` Thomas Gleixner
2014-06-16 22:28 ` Thomas Gleixner
2014-06-16 22:49 ` Darren Hart
2014-06-16 22:39 ` Darren Hart
2014-06-21 20:33 ` [tip:locking/core] " tip-bot for Thomas Gleixner
2014-06-11 20:45 ` [patch 3/5] futex: Split out the waiter check from lookup_pi_state() Thomas Gleixner
2014-06-16 18:12 ` Darren Hart
2014-06-21 20:33 ` [tip:locking/core] " tip-bot for Thomas Gleixner
2014-06-11 20:45 ` [patch 2/5] futex: Use futex_top_waiter() in lookup_pi_state() Thomas Gleixner
2014-06-16 16:51 ` Darren Hart
2014-06-21 20:33 ` [tip:locking/core] " tip-bot for Thomas Gleixner
2014-06-11 20:45 ` [patch 4/5] futex: Split out the first waiter attachment from lookup_pi_state() Thomas Gleixner
2014-06-16 18:19 ` Darren Hart
2014-06-21 20:33 ` [tip:locking/core] " tip-bot for Thomas Gleixner
2014-06-11 20:45 ` [patch 5/5] futex: Simplify futex_lock_pi_atomic() and make it more robust Thomas Gleixner
2014-06-13 5:46 ` Darren Hart
2014-06-13 8:34 ` Thomas Gleixner
2014-06-13 9:36 ` Thomas Gleixner
2014-06-13 9:44 ` [patch V2 " Thomas Gleixner
2014-06-13 20:51 ` Davidlohr Bueso
2014-06-16 20:36 ` Darren Hart
2014-06-17 7:20 ` Thomas Gleixner [this message]
2014-06-21 20:34 ` [tip:locking/core] " tip-bot for Thomas Gleixner
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