This is the mail archive of the
libc-alpha@sourceware.org
mailing list for the glibc project.
Re: [RFC v2 PATCH] futex: extend set_robust_list to allow 2 locking ABIs at the same time.
- From: Florian Weimer <fweimer at redhat dot com>
- To: Thomas Gleixner <tglx at linutronix dot de>
- Cc: Shawn Landden <shawn at git dot icu>, libc-alpha at sourceware dot org, linux-api at vger dot kernel dot org, LKML <linux-kernel at vger dot kernel dot org>, Arnd Bergmann <arnd at arndb dot de>, Deepa Dinamani <deepa dot kernel at gmail dot com>, Oleg Nesterov <oleg at redhat dot com>, Andrew Morton <akpm at linux-foundation dot org>, Catalin Marinas <catalin dot marinas at arm dot com>, Keith Packard <keithp at keithp dot com>, Peter Zijlstra <peterz at infradead dot org>
- Date: Tue, 05 Nov 2019 11:06:25 +0100
- Subject: Re: [RFC v2 PATCH] futex: extend set_robust_list to allow 2 locking ABIs at the same time.
- References: <20191104002909.25783-1-shawn@git.icu> <87woceslfs.fsf@oldenburg2.str.redhat.com> <alpine.DEB.2.21.1911051053470.17054@nanos.tec.linutronix.de>
* Thomas Gleixner:
> On Tue, 5 Nov 2019, Florian Weimer wrote:
>> * Shawn Landden:
>> > If this new ABI is used, then bit 1 of the *next pointer of the
>> > user-space robust_list indicates that the futex_offset2 value should
>> > be used in place of the existing futex_offset.
>>
>> The futex interface currently has some races which can only be fixed by
>> API changes. I'm concerned that we sacrifice the last bit for some
>> rather obscure feature. What if we need that bit for fixing the
>> correctness issues?
>
> That current approach is going nowhere and if we change the ABI ever then
> this needs to happen with all *libc folks involved and agreeing.
>
> Out of curiosity, what's the race issue vs. robust list which you are
> trying to solve?
Sadly I'm not trying to solve them. Here's one of the issues:
<https://sourceware.org/bugzilla/show_bug.cgi?id=14485>
I think there are others, but I can't find a reference to them. If
anyone wants to work on this, I can dig out the details and ask some
folks who have looked at this in the past.
Thanks,
Florian