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Date: Wed, 11 Mar 2009 17:50:35 +0000 (UTC) From: Dmitriy V'jukov <dvyukov@...il.com> To: linux-kernel@...r.kernel.org Subject: Re: RCU: Number of grace-periods Paul E. McKenney <paulmck <at> linux.vnet.ibm.com> writes: > > Interesting thought -- but please keep in mind that acquire/release fences > still allow subsequent stores to be reordered to precede earlier loads. > This means that the first loads in the RCU critical section could be > reordered to precede the final store of the rcu_read_lock() primitive. Hmmm... Yes, I've missed this moment. I think you are right. The critical synchronizing action of the __rcu_read_lock() is the store to the __get_cpu_var(rcu_flipctr) (not a load!). So some code from the critical section can hoist above the store to the __get_cpu_var(rcu_flipctr). However the good question is how many grace-periods is required if code can hoist above read_lock(), but can't sink below read_unlock()? Good work for Relacy :) Nope, I've not yet tried to apply it... -- Best regards, Dmitriy V'jukov -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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