On Mon, Apr 21, 2008 at 08:49:58AM -0700, Linus Torvalds wrote: > > That is *not* the main problem. > > If you use "rcu_dereference()" on the wrong access, it not only loses the > "smp_read_barrier_depends()" (which is a no-op on all sane architectures > anyway), but it loses the ACCESS_ONCE() thing *entirely*. Actually rcu_dereference didn't have ACCESS_ONCE when I did this. That only appearaed later with the preemptible RCU work. The original purpose of rcu_dereference was exactly to replace the explicit barriers that people were using for RCU, nothing more, nothing less. Oh and I totally agree that the compiler is going to generate insane code whenever ACCESS_ONCE is used. In this case we may have avoided it by rearranging the code, but in general the introduction of ACCESS_ONCE in rcu_dereference is likely to have a negative impact on the code generated. Remember that "volatile" discussion? I think this is where it all came from. Cheers, -- Visit Openswan at http://www.openswan.org/ Email: Herbert Xu ~{PmV>HI~} <herbert@xxxxxxxxxxxxxxxxxxx> Home Page: http://gondor.apana.org.au/~herbert/ PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
