On Wed, 26 Jan 2011 17:57:22 -0800
Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote:
> On Thu, 27 Jan 2011 10:43:39 +0900 KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> wrote:
>
> > --- mmotm-0125.orig/kernel/res_counter.c
> > +++ mmotm-0125/kernel/res_counter.c
> > @@ -126,10 +126,24 @@ ssize_t res_counter_read(struct res_coun
> > pos, buf, s - buf);
> > }
> >
> > +#if BITS_PER_LONG == 32
> > +u64 res_counter_read_u64(struct res_counter *counter, int member)
> > +{
> > + unsigned long flags;
> > + u64 ret;
> > +
> > + spin_lock_irqsave(&counter->lock, flags);
> > + ret = *res_counter_member(counter, member);
> > + spin_unlock_irqrestore(&counter->lock, flags);
> > +
> > + return ret;
> > +}
> > +#else
> > u64 res_counter_read_u64(struct res_counter *counter, int member)
> > {
> > return *res_counter_member(counter, member);
> > }
> > +#endif
>
> _irqsave is only needed if the lock will be taken from irq context.
> Does that happen?
>
I just obey current desing of res_counter, as bugfix.
This counter is designed to be safe against irq context.
Adding CC: to Balbir.
To be honest, it has never happened since res_counter is introduced. I imagine
there was a big plan when this counter was designed. But I think it will
be never called other than memcg because cpu, blkio controller haven't
use res_counter, finally. And memcg tends to use per-cpu counter because of
performance.
If I need to remove irq flags from this function, I'll do in another patch
which changes total design of res_counter and make it not safe agaisnt irq context.
Thanks,
-Kame
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