linux-kernel - Re: [Bug #11875] radeonfb lockup in .28-rc (bisected)

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Date:	Tue, 11 Nov 2008 12:49:34 +1100
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Andreas Schwab <schwab@...e.de>
Cc:	"Rafael J. Wysocki" <rjw@...k.pl>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Kernel Testers List <kernel-testers@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"David S. Miller" <davem@...emloft.net>,
	James Cloos <cloos@...loos.com>,
	Paul Collins <paul@...ly.ondioline.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [Bug #11875] radeonfb lockup in .28-rc (bisected)

On Tue, 2008-11-11 at 00:54 +0100, Andreas Schwab wrote:
> 
> > Can you describe your problem more precisely ?
> 
> It crashes during suspend (after the console was switched away from X),
> but I can only see a frame buffer with apparently random contents when
> it happens.  When suspend works then those random frame buffer contents
> are only briefly visible before the screen is cleared.

Does it actually switches away from X ?

IE. You see the console before the crap on console or not ?

I've seen what you describe happening when doing snooze -f (direct
kernel ioctl) straight from within X. It seems to me that the problem
was that for some reason it didn't switch the console, which would
definitely make it crash. I need to double check what's up, it's
possible that the kernel fails to switch it properly or fails to wait
for X to ack the switch.

In any case, I doesn't seem to be directly related to those radeonfb
changes, though a clash with X like that is indeed more likely to
actually happen if radeonfb relies more heavily on acceleration.

I'll have a look later today at the console switch from X in the kernel
see if it's been broken in a way or another.

Note: I just did some tests using both echo "mem" >/sys/power/state and
snooze -f and it worked fine. IE, the console switch away from X worked.
So while I think I observed your problem once, I also cannot reproduce
it now.

I wonder if there's a race condition in the VT switch. It's possible
that it could be yet another case of X whacking the chip after it has
effectively relinguished control of the VT to the kernel, or it could be
a kernel race.

Cheers,
Ben.

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