linux-kernel - Re: [PATCH] lockdep: Fix redundant_hardirqs

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Date:	Wed, 28 Apr 2010 17:12:06 +1000
From:	Stephen Rothwell <sfr@...b.auug.org.au>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Ingo Molnar <mingo@...e.hu>, LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	David Miller <davem@...emloft.net>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Subject: Re: [PATCH] lockdep: Fix redundant_hardirqs_on incremented with
 irqs enabled

Hi Frederic,

On Thu, 15 Apr 2010 15:37:50 +0200 Frederic Weisbecker <fweisbec@...il.com> wrote:
>
> When a path restore the flags while irqs are already enabled, we
> update the per cpu var redundant_hardirqs_on in a racy fashion
> and debug_atomic_inc() warns about this situation.
> 
> In this particular case, we need to explictly disable the irqs before
> updating this stat var in order to update it safely.
> 
> Reported-by: Stephen Rothwell <sfr@...b.auug.org.au>
> Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: David Miller <davem@...emloft.net>
> Cc: Benjamin Herrenschmidt <benh@...nel.crashing.org>
> ---
>  kernel/lockdep.c |    4 ++++
>  1 files changed, 4 insertions(+), 0 deletions(-)
> 
> diff --git a/kernel/lockdep.c b/kernel/lockdep.c
> index 78325f8..65d4336 100644
> --- a/kernel/lockdep.c
> +++ b/kernel/lockdep.c
> @@ -2298,7 +2298,11 @@ void trace_hardirqs_on_caller(unsigned long ip)
>  		return;
>  
>  	if (unlikely(curr->hardirqs_enabled)) {
> +		unsigned long flags;
> +
> +		raw_local_irq_save(flags);
>  		debug_atomic_inc(redundant_hardirqs_on);
> +		raw_local_irq_restore(flags);
>  		return;
>  	}
>  	/* we'll do an OFF -> ON transition: */

I applied this patch to linux-next today and it fixes my PowerPC boot
problems, so I will keep it in linux-next until it gets applied to the
tip tree or something better comes along.

Thanks.
-- 
Cheers,
Stephen Rothwell                    sfr@...b.auug.org.au
http://www.canb.auug.org.au/~sfr/

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