linux-kernel - Re: [PATCH 3/4]percpu_counter: fix code for 32bit systems

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:	Wed, 13 Apr 2011 09:05:36 +0800
From:	Shaohua Li <shaohua.li@...el.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	lkml <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"cl@...ux.com" <cl@...ux.com>
Subject: Re: [PATCH 3/4]percpu_counter: fix code for 32bit systems

On Wed, 2011-04-13 at 03:02 +0800, Tejun Heo wrote:
> On Tue, Apr 12, 2011 at 04:04:04PM +0800, Shaohua Li wrote:
> >  static inline s64 percpu_counter_read(struct percpu_counter *fbc)
> >  {
> > +#if BITS_PER_LONG == 32
> > +	s64 count;
> > +	spin_lock(&fbc->lock);
> > +	count = fbc->count;
> > +	spin_unlock(&fbc->lock);
> > +	return count;
> > +#else
> >  	return fbc->count;
> > +#endif
> 
> I don't know.  Is there any problem caused by this?  The interface is
> known to be unreliable and already being used in speculative manner.
> I think it's more beneficial to avoid using locks on fast read path.
yes, it is unreliable, but only in an extent of batch*nr_cpus. accessing
64bits in 32bit machine can give us a _very_ big inaccuracy, which is
unacceptable to me.

--
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/