Date: Thu, 24 Dec 1998 11:19:12 -0800 (PST) From: John Polstra <jdp@polstra.com> To: mike@smith.net.au Cc: current@FreeBSD.ORG Subject: Re: trap 12 with interrupts disabled Message-ID: <199812241919.LAA01894@vashon.polstra.com> In-Reply-To: <199812220225.SAA02191@dingo.cdrom.com>
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In article <199812220225.SAA02191@dingo.cdrom.com>,
Mike Smith <mike@smith.net.au> wrote:
> > >>> pid 281 (Xaccel): trap 12 with interupts disabled
> > >>
> > >> Yes, I've noticed this one too. It seems to have crept in relatively
> > >> recently, and strangely seems not to cause any problems.
> > >
> > > The diagnostic just warns of a bad situation (Xaccel has turned off
> > > interrupts for some reason, and then pagefaulted), it doesn't mention
> > > that it has in fact turned interrupts back on so that the pagefault can
> > > be safely completed.
> >
> > If my page fault fails because I've blocked the interrupt, I'd expect
> > some serious damage to happen to the process environment.n
>
> Usually you're lucky and something else turns them on unconditionally.
> This test simply makes damn sure that if you take a fault interrupts
> get turned back on.
I'm still not entirely clear about the implications of this change.
If I understand it right, the message is caused by a bug in Xaccel.
The message and the re-enabling of interrupts was added in revision
1.129 of trap.c. The message now isn't particularly rare if you're
running Xaccel. I got one almost immediately after updating my
kernel.
The bug didn't seem to hurt anything before. But now at least one
person is reporting hangs on a system running Xaccel. That concerns
me.
Do the interrupts get turned back off again when control returns to
Xaccel, or do they remain on? If Xaccel is assuming they're off, it
seems bad to turn them on underfoot.
Finally, do we have a contact at XiG to notify about this?
John
--
John Polstra jdp@polstra.com
John D. Polstra & Co., Inc. Seattle, Washington USA
"Nobody ever went broke underestimating the taste of the American public."
-- H. L. Mencken
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