linux-kernel - Re: [PATCH] [RFC] timerfd: add TFD_NOTIFY_CLOCK

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: <1291254957.2846.47.camel@work-vm>
Date:	Wed, 01 Dec 2010 17:55:57 -0800
From:	john stultz <johnstul@...ibm.com>
To:	Jamie Lokier <jamie@...reable.org>
Cc:	Valdis.Kletnieks@...edu, Lennart Poettering <mzxreary@...inter.de>,
	Alexander Shishkin <virtuoso@...nd.org>,
	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Feng Tang <feng.tang@...el.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Michael Tokarev <mjt@....msk.ru>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	Chris Friesen <chris.friesen@...band.com>,
	Kay Sievers <kay.sievers@...y.org>,
	"Kirill A. Shutemov" <kirill@...temov.name>,
	Artem Bityutskiy <dedekind1@...il.com>,
	Davide Libenzi <davidel@...ilserver.org>,
	linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH] [RFC] timerfd: add TFD_NOTIFY_CLOCK_SET to watch for
 clock changes

On Thu, 2010-12-02 at 01:18 +0000, Jamie Lokier wrote:
> Valdis.Kletnieks@...edu wrote:
> > On Wed, 01 Dec 2010 10:43:59 GMT, Jamie Lokier said:
> > 
> > > So maybe CLOCK_MONOTONIC should be changed to include elapsed time
> > > during suspend/resume, and CLOCK_MONOTONIC_RAW could remain as it is,
> > > for programs that want that?
> > 
> > Wouldn't that be an API break for programs that are expecting the current
> > behavior of CLOCK_MONOTONIC?  Yes, there should be a way to request either of
> > them - but if there's only one way now, it should continue to act the current
> > way, and the added way is the second option.
> 
> I don't know.  Can you think of any program which would break if
> suspend/resume's clocks behaved like ordinary task scheduling - when a
> task doesn't run for a long time because of scheduling decisions?
> Hmm, I guess some realtime apps might like to know.

Like I mentioned earlier, CLOCK_MONOTONIC_RAW and CLOCK_MONOTONIC are
tightly tied, so anything using CLOCK_MONOTONIC_RAW would break.

It might be possible to change both, but I still think such a change
would be bad.

> Currently CLOCK_MONOTONIC jumps forwards by 4 seconds on
> suspend/resume anyway (as seen by userspace), on my x86 laptop running
> 2.6.37-rc3.  So it does already jump a bit...

So just to clarify here, by this do you mean that there's ~4 seconds
delay between the resume event and when userland apps start to run (or
possibly some of that accumulating between the app freeze and the
timekeeping suspend) ?

Or are you seeing CLOCK_MONOTONIC jump 4 seconds out of sync with
CLOCK_REALTIME? 

It should be the delta between CLOCK_MONOTONIC and CLOCK_REALTIME prior
to suspend should be that same delta + suspend time after resume. If
that's not the case, something may be broken.

thanks
-john

--
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/