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Date: Wed, 21 Sep 2005 23:42:32 -0700
From: Andrew Morton <akpm@osdl.org>
To: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
Cc: Brice.Goglin@ens-lyon.org, linux-kernel@vger.kernel.org, rth@twiddle.net
Subject: Re: Kernel panic during SysRq-b on Alpha
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Ivan Kokshaysky <ink@jurassic.park.msu.ru> wrote:
>
> On Wed, Sep 21, 2005 at 03:11:07PM +0200, Brice Goglin wrote:
> > Kernel bug at kernel/printk.c:683
> > swapper(0): Kernel Bug 1
> > pc = [<fffffc000032706c>]  ra = [<fffffc00004352d4>]  ps = 0007    Not
> > tainted
> > pc is at acquire_console_sem+0x2c/0x90
> 
> Indeed, acquire_console_sem() does BUG() in interrupt context now,
> as in the case of SysRq-b.
> 
> Ivan.
> 
> --- linux/arch/alpha/kernel/process.c.orig	Mon Aug 29 03:41:01 2005
> +++ linux/arch/alpha/kernel/process.c	Thu Sep 22 09:51:26 2005
> @@ -127,6 +127,10 @@ common_shutdown_1(void *generic_ptr)
>  	/* If booted from SRM, reset some of the original environment. */
>  	if (alpha_using_srm) {
>  #ifdef CONFIG_DUMMY_CONSOLE
> +		/* If we've gotten here after SysRq-b, leave interrupt
> +		   context before taking over the console. */
> +		if (in_interrupt())
> +			irq_exit();
>  		/* This has the effect of resetting the VGA video origin.  */
>  		take_over_console(&dummy_con, 0, MAX_NR_CONSOLES-1, 1);

Wow, never seen that done before.  Does it actually work?  For keyboard,
serial console and /proc/sysrq-trigger?