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Date:      Thu, 04 Jun 2020 00:28:52 +0000
From:      bugzilla-noreply@freebsd.org
To:        bugs@FreeBSD.org
Subject:   [Bug 243225] "mpr0: Out of chain frames" boot hang after clang 9.0.1 import (probably timing, not compiler related)
Message-ID:  <bug-243225-227-Dl0LbstXOP@https.bugs.freebsd.org/bugzilla/>
In-Reply-To: <bug-243225-227@https.bugs.freebsd.org/bugzilla/>
References:  <bug-243225-227@https.bugs.freebsd.org/bugzilla/>

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=3D243225

--- Comment #5 from Terry Kennedy <terry-freebsd@glaver.org> ---
(In reply to Warner Losh from comment #4)

I tried increasing it and it doesn't help. This happens during the initial
device probe at boot time. We should only need chain frames if we're doing =
I/O
to a connected peripheral, and this error happens even without the tape dri=
ve
(or anything else) connected. Changing the slot the controller is in,
enabling/disabling hyperthreading, or sometimes just sitting at the loader
prompt before proceeding will make the problem disappear. My guess is that =
it
is a timing loop that is close to marginal, depending on the other hardware=
 in
the system. When the problem manifests, the system goes down the rabbit hol=
e of
"out of chain frames", probably because the code thinks the only reason for=
 an
error in that part of the path is running out of chain frames.

This is a Dell R730 (complete description in prior reply) so I can capture =
the
complete boot as a video and make the video (and player app) available if
anyone wants to look at it. Alternatively, I can provide remore access
(console, reset, etc) via the Dell iDRAC controller.

The problem has persisted from 12.0 to the latest 12-STABLE. All hardware is
up-to-date, Dell has replaced the controller multiple times and the tape dr=
ive
and cable once.

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