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SubjectRe: [PATCH 3/4]percpu_counter: fix code for 32bit systems
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Le mardi 12 avril 2011 à 16:04 +0800, Shaohua Li a écrit :
> percpu_counter.counter is a 's64'. Accessing it in 32-bit system is racing.
> we need some locking to protect it otherwise some very wrong value could be
> accessed.
>
> Signed-off-by: Shaohua Li <shaohua.li@intel.com>
> ---
> include/linux/percpu_counter.h | 43 +++++++++++++++++++++++++++++++----------
> 1 file changed, 33 insertions(+), 10 deletions(-)
>
> Index: linux/include/linux/percpu_counter.h
> ===================================================================
> --- linux.orig/include/linux/percpu_counter.h 2011-04-12 15:48:44.000000000 +0800
> +++ linux/include/linux/percpu_counter.h 2011-04-12 15:48:54.000000000 +0800
> @@ -54,7 +54,15 @@ static inline s64 percpu_counter_sum(str
>
> static inline s64 percpu_counter_read(struct percpu_counter *fbc)
> {
> +#if BITS_PER_LONG == 32
> + s64 count;
> + spin_lock(&fbc->lock);
> + count = fbc->count;
> + spin_unlock(&fbc->lock);
> + return count;
> +#else
> return fbc->count;
> +#endif
> }
>

Hmm... did you test this with LOCKDEP on ?

You add a possible deadlock here.

Hint : Some percpu_counter are used from irq context.

This interface assumes caller take the appropriate locking.



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