linux-kernel - Re: [RFC PATCH 1/4] watchdog: hpwdt: Don't disable watchdog on NMI

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Message-ID: <4f7de732-31cf-a220-f1eb-3d8182cf9c72@roeck-us.net>
Date:   Thu, 7 Feb 2019 20:17:29 -0800
From:   Guenter Roeck <linux@...ck-us.net>
To:     Jerry.Hoemann@....com, Ivan Mironov <mironov.ivan@...il.com>
Cc:     linux-watchdog@...r.kernel.org, linux-kernel@...r.kernel.org,
        Wim Van Sebroeck <wim@...ux-watchdog.org>
Subject: Re: [RFC PATCH 1/4] watchdog: hpwdt: Don't disable watchdog on NMI

On 2/7/19 5:26 PM, Jerry Hoemann wrote:
> On Sat, Feb 02, 2019 at 09:55:29AM +0500, Ivan Mironov wrote:
>> On Tue, 2019-01-15 at 19:27 -0700, Jerry Hoemann wrote:
>>> On Mon, Jan 14, 2019 at 07:36:14AM +0500, Ivan Mironov wrote:
>>
>> Somehow I missed the whole pretimout thing when reading about the
>> watchdog API. Thanks for clarification, now code makes much more sense
>> =).
>>
>> Still, I do not really understand the point of enabling of kdump
>> support in hpwdt driver by default while kdump is not enabled by
>> default.
> 
> Kdump is enabled by default by our Distro partners.
> 
> HPE works with distro partners to deliver a validated system which we support.
> 
> The ability to generate crash dumps is one of the means we use to
> support our customers.  Even if kdump isn't configured, panic will
> at least print stack trace to indicate system activity.
> 
> 
>>
>> Also, existing code may call hpwdt_stop() (and thus break watchdog)
>> even if pretimout is disabled.
>>
>> Also, "panic=N" option is not providing a way to *not* panic on NMI
>> unrelated with iLO. This could be circumvented by blacklisting the
>> hpwdt module entirely, but normal watchdog functionality would be lost
>> then.
> 
> panic=N provides for reset upon receipt of NMI if user wants timeout
> to reset system but not a crash dump.
> 
> The panic is for error containment.  On the legacy systems within
> the context of hpwdt_pretimeout we cannot determine if the error
> is recoverable or not.  So, we have little choice but to panic.
> 
> 
>>
>> It is possible to rebuild kernel without HPWDT_NMI_DECODING (which is
>> enabled in Fedora, for example). But it is nearly impossible to come to
>> this solution without examining the source code, because description of
>> this option does not mention that it is really about pretimout support
>> and panics and not about something else...
> 
> The name is not the best given its current use, but I'm not sure a
> name change would be allowed.
> 

I would be open to accepting an improved help text of this configuration
option. I am not going to entertain (or accept) a name change.
That would open up a can of worms, with everyone in the world requesting
name changes. That would be pretty pointless and make the kernel all but
unmanageable.

Guenter

> However, I will send a patch to update the documentation in Kconfig.
> 
>