linux-kernel - Re: [2.6.23-rc1 REGRESSION] CPU hotplug totally broken on HPC nx6325 (x86

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Date:	Thu, 26 Jul 2007 21:22:49 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Andi Kleen <ak@...e.de>, LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Pavel Machek <pavel@....cz>,
	Michal Piotrowski <michal.k.k.piotrowski@...il.com>
Subject: Re: [2.6.23-rc1 REGRESSION] CPU hotplug totally broken on HPC nx6325 (x86_64)

On Thursday, 26 July 2007 18:43, Linus Torvalds wrote:
> 
> On Thu, 26 Jul 2007, Rafael J. Wysocki wrote:
> >
> > On my Turion64-based HPC nx6325 with the 2.6.23-rc1 x86_64 kernel doing
> > 
> > # echo 0 > /sys/devices/system/cpu/cpu1/online
> > 
> > causes the system to crash in a spectacular fashion (call traces going
> > continuously on the console, no reaction to anything except for the power
> > button).  For this reason, suspend and hibernation don't work as well.
> 
> Yeah, I really shouldn't have applied that patch. I didn't notice that it 
> not only cleaned up the direct memcpy's, it also re-introduced the damn 
> broken code that we fixed once already.
> 
> Dammit, that read-only debug support IS NOT WORTH THIS CRAP.
> 
> I absolutely *detest* it when "debugging features" end up being the thing 
> that causes crashes. I think it shows a total lack of taste and 
> understanding, and I'm totally tired of it. This has happened too many 
> times.
> 
> Andi: please don't send this patch *ever* again. If a patch that is 
> supposed to help debugging just causes problems, that patch should be 
> thrown away FOREVER.
> 
> Andrew - on that same note: please throw away the dwarf traceback crap 
> from your tree that Andi is still apparently pushing. Exact same issue. 
> 
> Debugging "helper" code that has historically only caused problems. We 
> could equally well just enable frame pointers for debugging and add the 
> trivial code to follow that instead, and it would work (the way it has 
> worked on x86 basically forever).
> 
> Rafael, does reverting just this part (and leaving the "text_poke()" 
> cleanups) work for you?

Yes, it does, with the appended fix on top. :-)

Greetings,
Rafael


---
 arch/i386/kernel/alternative.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Index: linux-2.6.23-rc1/arch/i386/kernel/alternative.c
===================================================================
--- linux-2.6.23-rc1.orig/arch/i386/kernel/alternative.c
+++ linux-2.6.23-rc1/arch/i386/kernel/alternative.c
@@ -432,7 +432,7 @@ void __init alternative_instructions(voi
  */
 void __kprobes text_poke(void *oaddr, unsigned char *opcode, int len)
 {
-	memcpy(addr, opcode, len);
+	memcpy(oaddr, opcode, len);
 	sync_core();
 	/* Not strictly needed, but can speed CPU recovery up. Ignore cross cacheline
 	   case. */
-
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