linux-kernel - Re: 2.6.26-rc9-git4: Reported regressions from 2.6.25

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Date:	Thu, 10 Jul 2008 20:06:20 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Alexey Dobriyan <adobriyan@...il.com>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Kamalesh Babulal <kamalesh@...ux.vnet.ibm.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Adrian Bunk <bunk@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Natalie Protasevich <protasnb@...il.com>,
	Kernel Testers List <kernel-testers@...r.kernel.org>,
	"Paul E. McKenney" <paulmck@...ibm.com>
Subject: Re: 2.6.26-rc9-git4: Reported regressions from 2.6.25


* Ingo Molnar <mingo@...e.hu> wrote:

> cool! :)
> 
> (hm, could anyone please resend Nick's original mail? The original one 
> is not in my lkml folder nor on lkml.org - only the quoted one.)

ok, got the mail now now:

| | Annoyed this wasn't a crazy obscure error in the algorithm I could 
| | fix :) [...]

Paul recently ran a formal proof against all sorts of RCU details (and 
found and fixed a few obscure races that way that no-one ever 
triggered), so i'd be quite surprised if we found anything in the core 
algorithm :-)

| | [...] I spent all day debugging it and had to make a special test 
| | case (rcutorture didn't seem to trigger it), and a big RCU state 
| | logging infrastructure to log millions of RCU state transitions and 
| | events. Oh well.

nice debugging!

Acked-by: Ingo Molnar <mingo@...e.hu>

i'm wondering why rcutorture didnt trigger it. I do run !HOTPLUG + 
RCU_PREEMPT kernels and never saw this. Nor did Paul. That aspect is 
weird.

	Ingo
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