Subject: Re: "double" hpet clocksource && hard freeze [bisected]
From: john stultz <johnstul@us.ibm.com>
To: Bob Picco <bob.picco@hp.com>
Cc: "Luck, Tony" <tony.luck@intel.com>, Paolo Ornati <ornati@fastwebnet.it>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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Date: Fri, 24 Aug 2007 11:17:34 -0700
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On Fri, 2007-08-24 at 08:46 -0400, Bob Picco wrote:
> john stultz wrote:	[Thu Aug 23 2007, 05:41:45PM EDT]
> > On Thu, 2007-08-23 at 14:05 -0700, john stultz wrote:
> > > On Thu, 2007-08-23 at 13:41 -0700, Luck, Tony wrote:
> > > > > I have a double "hpet" entry in "available_clocksource":
> > > > >	$ cat /sys/devices/system/clocksource/clocksource0/available_clocksource
> > > > >	tsc hpet hpet acpi_pm jiffies
> > > > 
> > > > Oops.  If seems that both drivers/char/hpet.c and arch/x86_64/kernel/hpet.c
> > > > both register a clocksource named "hpet".  Probably a result of bringing
> > > > back to life a long lost patch, and having someone else (John Stultz, according
> > > > to git blame) make a similar change to a different file in the intervening
> > > > time.
> > > > 
> > > > Presumably the thing to do would be merge the x86_64 specific version
> > > > into the drivers/char/hpet.c version?
> > > 
> > > Ugh. Yea. i386 has an hpet clocksource as well. We should kill the
> > > duplication, but at the moment I'm not comfortable that the
> > > driver/char/hpet.c is ok to be used for i386/x86_64 (Bob: Do you know
> > > why the shift value is only 10?).
> > > 
> > > 
> > > I'm a little surprised by this, as the clocksource code use to prevent
> > > duplicate named clocksources from being registered, so I'm not sure how
> > > that check got dropped.  Also I'm not quite sure I see where the hard
> > > freeze is coming from.
> > > 
> > > My initial reaction would be to either ifdef ia64 implementation in
> > > drivers/char/hpet.c or move the code under the ia64 arch dir until it is
> > > really usable by all arches.
> > 
> > Here is a possible quick fix. I'm open to other approaches, but I also
> > want to avoid too much churn before 2.6.23 goes out.
> > 
> > Paolo, could you verify this fixes the issue for you?
> > 
> > thanks
> > -john
> > 
> [snip]
> 
> I saw what was missed by me in my brief examination of this last night.
> The platform registers the hpet clocksource too.
> 
> Instead of adding the config flag to hpet driver, how about the patch
> below? Since you already check for duplication by address then adding
> a check for by name too seems okay to me.
> 
> bob
> 
> 
> Prevent duplicate names being registered with clocksource. This also
> eliminates the duplication of hpet clock registration when the arch
> uses the hpet timer and the hpet driver does too. The patch was
> compile and link tested.

Yea. While I'm still not completely comfortable leaving this up to boot
order alone (the ia64 hpet clocksource is clearly causing issues on
x86_64), I think this patch is something we need as well.

> 
> Signed-off-by: Bob Picco <bob.picco@hp.com>

Acked-by: John Stultz <johnstul@us.ibm.com>

>  kernel/time/clocksource.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> Index: linux-2.6.23-rc3/kernel/time/clocksource.c
> ===================================================================
> --- linux-2.6.23-rc3.orig/kernel/time/clocksource.c	2007-08-23 16:44:03.000000000 -0400
> +++ linux-2.6.23-rc3/kernel/time/clocksource.c	2007-08-24 08:36:41.000000000 -0400
> @@ -281,7 +281,7 @@ static int clocksource_enqueue(struct cl
>  		struct clocksource *cs;
> 
>  		cs = list_entry(tmp, struct clocksource, list);
> -		if (cs == c)
> +		if (cs == c || !strcmp(cs->name, c->name))
>  			return -EBUSY;
>  		/* Keep track of the place, where to insert */
>  		if (cs->rating >= c->rating)

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