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To: Andriy Gapon <avg@FreeBSD.org>
cc: freebsd-arch@FreeBSD.org
Subject: Re: watchdog end-user interface
In-reply-to: <ec3dfab5-c3bc-e9e5-181e-8c2704f60acd@FreeBSD.org>
From: "Poul-Henning Kamp" <phk@phk.freebsd.dk>
References: <ec3dfab5-c3bc-e9e5-181e-8c2704f60acd@FreeBSD.org>
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Date: Wed, 19 Oct 2016 11:18:18 +0000
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--------
In message <ec3dfab5-c3bc-e9e5-181e-8c2704f60acd@FreeBSD.org>, Andriy Gapo=
n wri
tes:

>I want to question if those options really belong to watchdogd.
>When a watchdog timer expires that results in a system-wide action (like =
a
>system reset).  To me, that implies that there should be a single system-=
wide
>configuration point.  And I am not sure that the daemon is the best choic=
e for it.

The reason I originally put it in a daemon, was to have the watchdog
implicitly test the kernels ability to schedule trivial processes.

It used to be, and may still be so that, there are deadlocks where
the kernel was twiddling its thumbs but userland did not progress.
Typical triggers for this are disk-I/O errors, corrupt filesystems,
memory overcommit etc.

A kernel-only watchdog patter would not trigger in that case.


-- =

Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    =

Never attribute to malice what can adequately be explained by incompetence=
.