linux-kernel - Re: [RFC][PATCH] clocksource: avoid unnecessary overflow in cyclecounter

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, 04 Mar 2014 08:31:20 +0100
From:	Mike Galbraith <bitbucket@...ine.de>
To:	Henrik Austad <henrik@...tad.us>
Cc:	John Stultz <johnstul@...ibm.com>, Salman Qazi <sqazi@...gle.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC][PATCH] clocksource: avoid unnecessary overflow in
 cyclecounter_cyc2ns()

On Tue, 2014-03-04 at 08:20 +0100, Henrik Austad wrote: 
> On Tue, Mar 04, 2014 at 06:20:09AM +0100, Mike Galbraith wrote:
> > Greetings,
> > 
> > While rummaging around looking for HTH a gaggle of weird a$$ machines
> > can manage to timewarp back and forth by exactly 208 days, I stumbled
> > across $subject which looks like it may want to borrow Salman's fix.
> > 
> > clocksource: avoid unnecessary overflow in cyclecounter_cyc2ns()
> > 
> > As per 4cecf6d401a "sched, x86: Avoid unnecessary overflow in sched_clock",
> > cycles * mult >> shift is overflow prone. so give it the same treatment.
> > 
> > Cc: Salman Qazi <sqazi@...gle.com>
> > Cc: John Stultz <johnstul@...ibm.com>
> > Signed-off-by: Mike Galbraith <bitbucket@...ine.de>
> > ---
> >  include/linux/clocksource.h |   11 ++++++++---
> >  1 file changed, 8 insertions(+), 3 deletions(-)
> > 
> > --- a/include/linux/clocksource.h
> > +++ b/include/linux/clocksource.h
> > @@ -77,13 +77,18 @@ struct timecounter {
> >   *
> >   * XXX - This could use some mult_lxl_ll() asm optimization. Same code
> >   * as in cyc2ns, but with unsigned result.
> > + *
> > + * Because it is the same as x86 __cycles_2_ns, give it the same treatment as
> > + * commit 4cecf6d401a "sched, x86: Avoid unnecessary overflow in sched_clock"
> > + * to avoid a potential cycles * mult overflow.
> 
> Do we normally reference a particular commit in a comment? Why not just 
> grab the same comment and add a "this is grabbed from arch/x86/... ?

Fewer '+' signs?  History doesn't go away, so seems fine to me.

-Mike

--
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/