linux-kernel - Re: BSOD

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Message-ID: <17919.42767.233797.860230@cargo.ozlabs.ibm.com>
Date:	Tue, 20 Mar 2007 20:19:11 +1100
From:	Paul Mackerras <paulus@...ba.org>
To:	David Miller <davem@...emloft.net>
Cc:	jesse.barnes@...el.com, zaitcev@...hat.com, jg@...top.org,
	linux-kernel@...r.kernel.org
Subject: Re: BSOD

David Miller writes:

> Mode setting is complex and it is not going to work exactly when you
> need the kernel crash message the most.

It's a matter of writing maybe a dozen MMIO registers on the ATI
chips, for instance, with some delays.  Provided we have interrupts
disabled and udelay still works, there's not a lot of the kernel that
we need to rely on to do that.

> After debugging the kernel for 10+ years I can tell you one thing, for
> a bad crash what's going to happen is you'll get the printk but that's
> about all that will work at that point, and the kernel is going to
> hang next.  Sometimes you won't get the whole panic message, just
> the beginning, even with the most simplistic printk implementation.
> 
> You will not, I repeat, will not be able to mode switch or anything
> non-trivial like that when the kernel is in this state.
> 
> Mode switching on panic, just say no. :-)

Anything is better than nothing.  At the moment we get nothing if you
are in X when the panic occurs, even for the nicest, most well-behaved
panics. :)  If we can change that to getting something sometimes,
that's a win.

Paul.
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