From: Dave Jiang <djiang@mvista•com>
To: Geoff Levand <geoffrey.levand@am•sony.com>
Cc: linuxppc-dev@ozlabs•org
Subject: Re: [RFC] BOOKE watchdog and kexec
Date: Tue, 22 May 2007 17:29:22 -0700 [thread overview]
Message-ID: <46538AE2.6010607@mvista.com> (raw)
In-Reply-To: <4653886A.30800@am.sony.com>
Geoff Levand wrote:
> Dave Jiang wrote:
>> What would be the appropriate way to deal with the BOOKE watchdog in order to
>> properly kexec? The BOOKE watchdog cannot be disabled. With the current
>> implementation, a watchdog daemon in userland is required to poke the
>> /dev/watchdog continously in order to keep it from going off. In the kexec
>> situation, the watchdog daemon in userland goes away when the new kernel is
>> executed. It is very possible that the new kernel can potentially timeout on a
>> certain hardware device initialization (i.e. SCSI discovery/timeout) and causes
>> the watchdog to go off and reset the hardware. The reset is of course not
>> wanted in this situation.
>
> I would think the same situation exists when the bootloader loads the first
> kernel. If that works, then you should be able to use the same mechanism to
> get the second kernel up.
>
> -Geoff
>
Not really. The bootloader starts from a hardware reset. The watchdog is off
from a hardware reset. The kernel driver has to specifically turn the watchdog
on either via kernel command line or by opening the watchdog device
/dev/watchdog right now. So technically this issue already exists even without
kexec. If the watchdog is turned on via kernel parameter and we hit a device
initialization timeout that takes too long, then we will get a watchdog reset.
There is a period of uncertainty between the watchdog turning on and when the
userland watchdog daemon is started with the current implementation.
--
------------------------------------------------------
Dave Jiang
Software Engineer
MontaVista Software, Inc.
http://www.mvista.com
------------------------------------------------------
next prev parent reply other threads:[~2007-05-23 0:29 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-05-22 23:53 [RFC] BOOKE watchdog and kexec Dave Jiang
2007-05-23 0:18 ` Geoff Levand
2007-05-23 0:29 ` Dave Jiang [this message]
2007-05-23 3:36 ` Michael Ellerman
2007-05-23 6:10 ` Kumar Gala
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