On 03/24/2014 01:25 PM, Eric Dumazet wrote: > On Mon, 2014-03-24 at 07:09 +0200, Michael S. Tsirkin wrote: > >> Seems an incredibly strict requirement for something that just >> silences a warning. >> What exactly should I test? >> I intended to just verify this produces same code as before >> d322f45ceed525daa under a recent gcc. > > Thats because many rcu_assign_pointer(X, NULL) were already converted to > RCU_INIT_POINTER(X, NULL) > > Quite frankly I don't know why you bother at all. > > Adding back the lazy test in rcu_assign_pointer() doesn't help to make > the API cleaner and easier to understand. > > People are usually using RCU API without really understanding > all the issues. They tend to add superfluous barriers because they feel > better. > > Having separate RCU_INIT_POINTER() and rcu_assign_pointer() serve as > better documentation of the code, I find it more easier to immediately > check what is going on while reviewing stuff. > > Presumably, checkpatch.pl could be augmented to suggest to use > RCU_INIT_POINTER(X, NULL) instead of rcu_assign_pointer(X, NULL)
I prefer rcu_assign_pointer(X, NULL) than RCU_INIT_POINTER(X, NULL), NULL should not be a special pointer value to the users of RCU. the RCU implements should hide the difference if RCU implements differentiate the values for optimization. RCU_INIT_POINTER() sounds as an initialization-stage API. If we need something different for NULL pointer, I prefer rcu_assign_*null*_pointer(). rcu_assign_pointer(X, NULL) implies compiler barrier(), but RCU_INIT_POINTER(X, NULL) doesn't. > > > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majord...@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
