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Date: Thu, 1 Aug 2002 14:52:16 -0600
Message-Id: <200208012052.g71KqG311998@vindaloo.ras.ucalgary.ca>
From: Richard Gooch <rgooch@ras.ucalgary.ca>
To: Willy TARREAU <willy@w.ods.org>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>,
       Marcelo Tosatti <marcelo@conectiva.com.br>,
       lkml <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] solved APM bug with -rc5
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Willy TARREAU writes:
> I finally got rid of it ! I now understand why it hanged randomly, and
> why I spent lots of time adding/removing unrelated patches. It's because
> in apm=power-off mode (SMP), a kernel thread is started for the apm()
> function, which does bios calls. And sometimes, the bios is called from
> CPU >0, which my bios doesn't like at all, thus explaining why the oopses
> were corrupted.
[...]
> diff -urN linux-2.4.19-rc5/arch/i386/kernel/apm.c linux-2.4.19-rc5-fix/arch/i386/kernel/apm.c
> --- linux-2.4.19-rc5/arch/i386/kernel/apm.c	Thu Aug  1 22:07:39 2002
> +++ linux-2.4.19-rc5-fix/arch/i386/kernel/apm.c	Thu Aug  1 22:26:56 2002
> @@ -1661,6 +1661,17 @@
>  	strcpy(current->comm, "kapmd");
>  	sigfillset(&current->blocked);
>  
> +#ifdef CONFIG_SMP
> +	/* 2002/08/01 - WT
> +	 * This is to avoid random crashes at boot time during initialization
> +	 * on SMP systems in case of "apm=power-off" mode. Seen on ASUS A7M266D.
> +	 * Some bioses don't like being called from CPU != 0.
> +	 */
> +	while (cpu_number_map(smp_processor_id()) != 0) {
> +		schedule();
> +	}
> +#endif
> +	

Hm. I bet you didn't try this with CONFIG_PREEMPT=y, right? IIRC, the
wonderful world of preemption means that you can get rescheduled on
another CPU without warning, unless you take a lock or explicitely
disable preemption.

				Regards,

					Richard....
Permanent: rgooch@atnf.csiro.au
Current:   rgooch@ras.ucalgary.ca
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