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Date:      Wed, 07 Oct 1998 16:27:17 -0600
From:      Brett Glass <brett@lariat.org>
To:        hackers@FreeBSD.ORG
Subject:   Another instance of the crash I was seeing
Message-ID:  <4.1.19981007162637.04032380@mail.lariat.org>

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Just a few days ago, Jim Dennis of Starshine encountered exactly the same
crash I've been experiencing here (with FreeBSD 2.2.7). As you may recall,
our backup script, which piped dump through gzip to ftp, was causing the
machine to crash with a seg fault. The debugger said that the seg fault
occurred in the kernel while it was in an idle loop.... Possibly waiting
for completion of an IDE command. (I suspect this is indeed where the
problem occurred, because the machine actually had a lot of work to do in
userland at the time; CPU usage was pegged. But the IDE driver blocks and
busy-waits for command completion in the kernel, so we would see it enter
the idle loop while it was waiting.) 

My SWAG is that the problem is most likely in the IDE/ATAPI or ed0 drivers,
and/or in interrupt handling during the busy wait. But I have no idea how
to figure out where the problem is.

Jim's crashes, like the ones I've been seeing, occurred while dumping disk
data to and from the network under relatively high CPU loads. He posted a
description to -questions recently.

Has anyone else seen this? It's beginning to look like a pattern, and we
need to nail it so that we can reinstate our backup procedure. (The one
we're using now is a stopgap.)

--Brett


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