linux-kernel - Re: [PATCH] kexec: yield to scheduler when loading kimage segments

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Message-ID: <87bmcgsui0.fsf@xmission.com>
Date:   Mon, 11 Jun 2018 19:45:11 -0500
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     "Farnitano\, Jarrett" <jmf@...zon.com>
Cc:     "kexec\@lists.infradead.org" <kexec@...ts.infradead.org>,
        "linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] kexec: yield to scheduler when loading kimage segments

"Farnitano, Jarrett" <jmf@...zon.com> writes:

>> On 6/11/18, 4:00 PM, "Eric W. Biederman" <ebiederm@...ssion.com> wrote:
>> 
>>     Is there a practical problem with unresponsiveness?  You are talking
>>     an embedded machine and rarely are there people in front of embedded
>>     computers these days.
>
> I did run into a practical problem. Hardware watchdogs on embedded
> systems can have short timers on the order of seconds. If the system
> is locked up for a few seconds with only a single core available, the
> watchdog may not be pet in a timely fashion. If this happens, the
> hardware watchdog will fire and reset the system.
>
> This really only becomes a problem when you are working with a single
> core, a decently sized initrd, and have a constrained hardware
> watchdog.

That would do it.

My foggy memory says this was not included back in the days where
cond_resched was spelled "if (need_resched) schedule();"  There were
concerns with spreading that too thin.  cond_resched in this path seems
as reasonable as anything.

Eric