linux-kernel - Re: [BUG] 2.6.37-rc3 massive interactivity regression on ARM

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <alpine.DEB.2.00.1012101344570.13986@router.home>
Date:	Fri, 10 Dec 2010 13:51:23 -0600 (CST)
From:	Christoph Lameter <cl@...ux.com>
To:	Peter Zijlstra <peterz@...radead.org>
cc:	Eric Dumazet <eric.dumazet@...il.com>,
	Venkatesh Pallipadi <venki@...gle.com>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	Mikael Pettersson <mikpe@...uu.se>,
	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	John Stultz <johnstul@...ibm.com>
Subject: Re: [BUG] 2.6.37-rc3 massive interactivity regression on ARM

On Fri, 10 Dec 2010, Peter Zijlstra wrote:

> > > gcc wont be able to do this yet (%fs/%gs selectors)
> >
> > The kernel can do that using the __percpu annotation.
>
> That's not true:
>
> # define __percpu
>
> Its a complete NOP.

The annotation serves for sparse checking. .... If you do not care about
those checks then you can simply pass a percpu pointer in the same form as
a regular pointer.

> > > But we can provide this_cpu_write_seqcount_{begin|end}()
> >
> > No we cannot do hat. this_cpu ops are for per cpu data and not for locking
> > values shared between processors. We have a mechanism for passing per cpu
> > pointers with a corresponding annotation.
>
> -enoparse, its not locking anything, is a per-cpu sequence count.

seqlocks are for synchronization of objects on different processors.

Seems that you do not have that use case in mind. So a seqlock restricted
to a single processor? If so then you wont need any of those smp write
barriers mentioned earlier. A simple compiler barrier() is sufficient.





--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/