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SubjectRe: [patch v3 2/3] percpu_counter: fix code for 32bit systems for UP
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On Thu, 2011-04-14 at 10:35 +0800, Eric Dumazet wrote:
> Le jeudi 14 avril 2011 à 10:04 +0800, shaohua.li@intel.com a écrit :
> > pièce jointe document texte brut (percpu-counter-32bits.patch)
> > 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 | 37 ++++++++++++++++++++++++++-----------
> > 1 file changed, 26 insertions(+), 11 deletions(-)
> >
> > Index: linux/include/linux/percpu_counter.h
> > ===================================================================
> > --- linux.orig/include/linux/percpu_counter.h 2011-04-14 08:50:45.000000000 +0800
> > +++ linux/include/linux/percpu_counter.h 2011-04-14 09:09:14.000000000 +0800
> > @@ -89,9 +89,20 @@ struct percpu_counter {
> > s64 count;
> > };
> >
> > -static inline int percpu_counter_init(struct percpu_counter *fbc, s64 amount)
> > +static inline void percpu_counter_set(struct percpu_counter *fbc, s64 amount)
> > {
> > +#if BITS_PER_LONG == 32
> > + preempt_disable();
> > fbc->count = amount;
> > + preempt_enable();
> > +#else
> > + fbc->count = amount;
> > +#endif
> > +}
> > +
> > +static inline int percpu_counter_init(struct percpu_counter *fbc, s64 amount)
> > +{
> > + percpu_counter_set(fbc, amount);
> > return 0;
> > }
> >
>
> Please dont do this and obfuscate the code.
>
> percpu_counter_init() cannot be racy.
>
> Its like saying spin_lock_init() could be racy.
>
> No other thread/cpu is supposed to use the object if not yet
> initialized.
that's true. I just want the code looks consistent and this doesn't
really obfuscate the code to me.

Thanks,
Shaohua

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