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

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Date:	Thu, 10 Jul 2008 15:02:14 +0400
From:	Alexey Dobriyan <adobriyan@...il.com>
To:	Nick Piggin <nickpiggin@...oo.com.au>
Cc:	"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>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Natalie Protasevich <protasnb@...il.com>,
	Kernel Testers List <kernel-testers@...r.kernel.org>
Subject: Re: 2.6.26-rc9-git4: Reported regressions from 2.6.25

On Thu, Jul 10, 2008 at 05:25:35PM +1000, Nick Piggin wrote:
> > Bug-Entry	: http://bugzilla.kernel.org/show_bug.cgi?id=10629
> > Subject		: 2.6.26-rc1-$sha1: RIP __d_lookup+0x8c/0x160
> > Submitter	: Alexey Dobriyan <adobriyan@...il.com>
> > Date		: 2008-05-05 09:59 (65 days old)
> > References	: http://lkml.org/lkml/2008/5/5/28
> > Handled-By	: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> 
> Attached is my fix for this problem. I don't think it is a regression
> as such, but it can't hurt to go into 2.6.26 IMO.

> PREEMPT_RCU without HOTPLUG_CPU is broken.

Bastard!

rcutorture fixed here, starting cross-compile stuff (without much interest).

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

> --- linux-2.6.orig/kernel/rcupreempt.c
> +++ linux-2.6/kernel/rcupreempt.c
> @@ -925,26 +925,22 @@ void rcu_offline_cpu(int cpu)
>  	spin_unlock_irqrestore(&rdp->lock, flags);
>  }
>  
> -void __devinit rcu_online_cpu(int cpu)
> -{
> -	unsigned long flags;
> -
> -	spin_lock_irqsave(&rcu_ctrlblk.fliplock, flags);
> -	cpu_set(cpu, rcu_cpu_online_map);
> -	spin_unlock_irqrestore(&rcu_ctrlblk.fliplock, flags);
> -}
> -
>  #else /* #ifdef CONFIG_HOTPLUG_CPU */
>  
>  void rcu_offline_cpu(int cpu)
>  {
>  }
>  
> -void __devinit rcu_online_cpu(int cpu)
> +#endif /* #else #ifdef CONFIG_HOTPLUG_CPU */
> +
> +void __cpuinit rcu_online_cpu(int cpu)
>  {
> -}
> +	unsigned long flags;
>  
> -#endif /* #else #ifdef CONFIG_HOTPLUG_CPU */
> +	spin_lock_irqsave(&rcu_ctrlblk.fliplock, flags);
> +	cpu_set(cpu, rcu_cpu_online_map);
> +	spin_unlock_irqrestore(&rcu_ctrlblk.fliplock, flags);
> +}
>  
>  static void rcu_process_callbacks(struct softirq_action *unused)
>  {


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