linux-kernel - Re: [Linux 2.6.28-rc4] BUG: using smp_processor_id() in preemptible [00000000] code: suspend_to

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Date:	Wed, 12 Nov 2008 10:56:00 -0800 (PST)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Maciej Rutecki <maciej.rutecki@...il.com>,
	Ingo Molnar <mingo@...e.hu>
cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	"lenb@...nel.org" <lenb@...nel.org>, linux-acpi@...r.kernel.org
Subject: Re: [Linux 2.6.28-rc4] BUG: using smp_processor_id() in preemptible
 [00000000] code: suspend_to_disk/2934

On Wed, 12 Nov 2008, Maciej Rutecki wrote:

> -rc3 works OK
> 
> I have this bug during suspend to disk:
> 
> [  188.592151] Enabling non-boot CPUs ...
> [  188.592151] SMP alternatives: switching to SMP code
> [  188.666058] BUG: using smp_processor_id() in preemptible [00000000]
> code: suspend_to_disk/2934
> [  188.666064] caller is native_sched_clock+0x2b/0x80

The cause seems to be commit 7cbaef9c83e58bbd4bdd534b09052b6c5ec457d5, 
"sched: optimize sched_clock() a bit" by Ingo.

Which actually comments on the fact that a few callers may need to be 
updated. That wasn't good. Ingo - it's not acceptable for a latish-rc 
patch to introduce _known_ bugs and not fixing everything up.

Of course, since Maciej has frame pointers disabled, the stack trace isn't 
entirely reliable, but it looks like the problem is "init_idle()".

That thing needs to call sched_clock() with interrupts disabled. Looking 
at it, I'd also expect that it should have used "sched_clock_cpu()", but 
I'm leaving that to Ingo to sort out. Ingo?

		Linus
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