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SubjectRe: [PATCH] lockdep: Fix redundant_hardirqs_on incremented with irqs enabled
Hi Frederic,

On Thu, 15 Apr 2010 15:37:50 +0200 Frederic Weisbecker <fweisbec@gmail.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@canb.auug.org.au>
> Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: David Miller <davem@davemloft.net>
> Cc: Benjamin Herrenschmidt <benh@kernel.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@canb.auug.org.au
http://www.canb.auug.org.au/~sfr/
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