linux-kernel - RE: "double" hpet clocksource && hard freeze [bisected]

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Date:	Fri, 24 Aug 2007 09:04:22 -0700
From:	"Luck, Tony" <tony.luck@...el.com>
To:	"Paolo Ornati" <ornati@...twebnet.it>,
	"Bob Picco" <bob.picco@...com>
Cc:	"john stultz" <johnstul@...ibm.com>,
	"Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>,
	"Bob Picco" <bob.picco@...com>
Subject: RE: "double" hpet clocksource && hard freeze [bisected]

> > 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.
>
> This one works too.

It is good to avoid registering two clocksources with the same name, but
the fix might be a bit more fragile than the eariler one that temporarily
marked the drivers/char/hpet.c one as CONFIG_IA64 only.  Given that the
hang went away when you applied the earlier patch, I conclude that the
drivers/char/hpet.c code is the one that got selected when you had two
"hpet" entries ... and that there is something wrong with that code that
doesn't work right on x86_64.  The fix to prevent registering a duplicate
name is presumably working for you simply because arch/x86_64/kernel/hpet.c
happens to get there first with its "hpet", so the drivers/char/hpet.c one
is dropped.  If something changed that reversed the order of these registrations,
then you'd get the "hpet" clocksource that results in a hang.

-Tony
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