linux-kernel - Re: [PATH -mm -v2] Fix a race condtion of oops_in

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]

Date:	Tue, 11 Nov 2008 09:05:18 +0800
From:	Huang Ying <ying.huang@...el.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	Chris Snook <csnook@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATH -mm -v2] Fix a race condtion of oops_in_progress

On Mon, 2008-11-10 at 15:35 +0800, KOSAKI Motohiro wrote:
> > > > As far as I know, barriers don't cause changes to be visible on other
> > > > CPUs faster too. It just guarantees corresponding operations after will
> > > > not get executed until that before have finished. And, I don't think we
> > > > need make changes to be visible on other CPUs faster.
> > > 
> > > You're correct that barrier() has no impact on other CPUs.  wmb() and rmb() do. 
> > >   If we don't need to make changes visible any faster, what's the point in using 
> > > atomic_set()?  It's not any less racy.  atomic_inc() and atomic_dec() would be 
> > > less racy, but you're not using those.
> > 
> > In default bust_spinlocks() implementation in lib/bust_spinlocks.c,
> > atomic_inc() and atomic_dec_and_test() is used. Which is used by x86
> > too. In some other architecture, atomic_set() is used to replace
> > "oops_in_progress = <xxx>". So this patch fixes architectures which use
> > default bust_spinlocks(), other architectures can be fixed by
> > corresponding architecture developers.
> 
> I think Chris is right.
> So, I reccomend to read Documentation/memory-barriers.txt
> 
> Almost architecture gurantee atomic_inc cause barrier implicitly.
> but not _all_ architecture.

Yes. atomic_inc() doesn't imply barrier on all architecture. But we
should not add barriers before all atomic_inc(), just ones needed. Can
you figure out which ones in the patch should has barrier added?

Best Regards,
Huang Ying


Download attachment "signature.asc" of type "application/pgp-signature" (198 bytes)