From: Yury Polyanskiy <ypolyans@princeton.edu>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Joel Becker <joel.becker@oracle.com>,
linux-kernel@vger.kernel.org, john stultz <johnstul@us.ibm.com>,
Jan Glauber <jan.glauber@de.ibm.com>
Subject: Re: [PATCH] hangcheck-timer is broken on x86
Date: Fri, 26 Mar 2010 17:52:01 -0400 [thread overview]
Message-ID: <20100326175201.3dbac6ce@penta.localdomain> (raw)
In-Reply-To: <20100326142423.1334d407.akpm@linux-foundation.org>
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On Fri, 26 Mar 2010 14:24:23 -0700
Andrew Morton <akpm@linux-foundation.org> wrote:
> On Tue, 23 Mar 2010 23:36:11 -0400
> Yury Polyanskiy <ypolyans@princeton.edu> wrote:
>
> > The drivers/char/hangcheck-timer.c is doubly broken. First, the
> > following line overflows unsigned long:
> > # define TIMER_FREQ (HZ*loops_per_jiffy)
> >
> > Second, and more importantly, loops_per_jiffy has little to do with the conversion from the
> > the time scale of get_cycles() (aka rdtsc) to the time scale of jiffies.
>
> It's a bit odd to have a driver be this broken on x86_32 for five years
> without anyone noticing. What are the user-visible effects of these
> shortcomings?
When the overflown value of TIMER_FREQ is abnormally low, it spams the
syslog with KERN_CRIT messages "Hangcheck: hangcheck value past margin!"
But whether it happens or not depends on HZ and lpj in a complex way.
People have hit it occasionally as far as google search can tell.
>
> Also, please do send us a Signed-off-by: for this patch, as explained
> in Documentation/SubmittingPatches, thanks.
>
Sorry.
Signed-off-by: Yury Polyanskiy <polyanskiy@gmail.com>
Thank you Andrew!
Yury
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next prev parent reply other threads:[~2010-03-26 21:52 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-03-24 3:36 [PATCH] hangcheck-timer is broken on x86 Yury Polyanskiy
2010-03-26 21:24 ` Andrew Morton
2010-03-26 21:52 ` Yury Polyanskiy [this message]
2010-03-26 21:46 ` Joel Becker
2010-03-26 22:00 ` Yury Polyanskiy
2010-03-27 0:57 ` Joel Becker
2010-03-27 2:02 ` Yury Polyanskiy
2010-03-27 22:03 ` Joel Becker
2010-03-27 22:51 ` Yury Polyanskiy
2010-03-27 23:36 ` Joel Becker
2010-03-28 2:08 ` Yury Polyanskiy
2010-03-29 1:00 ` john stultz
2010-03-29 14:11 ` Yury Polyanskiy
2010-03-29 16:43 ` john stultz
2010-03-29 17:04 ` Yury Polyanskiy
2010-03-29 18:44 ` john stultz
2010-03-29 19:53 ` Joel Becker
2010-03-29 21:08 ` Yury Polyanskiy
2010-03-29 21:43 ` john stultz
2010-03-29 22:34 ` Yury Polyanskiy
2010-04-08 0:52 ` Joel Becker
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