On Wed, Oct 09, 2013 at 05:28:33PM -0700, Paul E. McKenney wrote: > On Wed, Oct 09, 2013 at 05:12:40PM -0700, Eric Dumazet wrote: > > On Wed, 2013-10-09 at 16:40 -0700, Josh Triplett wrote: > > > > > that. Constructs like list_del_rcu are much clearer, and not > > > open-coded. Open-coding synchronization code is almost always a Bad > > > Idea. > > > > OK, so you think there is synchronization code. > > > > I will shut up then, no need to waste time. > > As you said earlier, we should at least get rid of the memory barrier > as long as we are changing the code.
Interesting thread! Sorry to chime in and asking a question: Why do we need an ACCESS_ONCE here if rcu_assign_pointer can do without one? In other words I wonder why rcu_assign_pointer is not a static inline function to use the sequence point in argument evaluation (if I remember correctly this also holds for inline functions) to not allow something like this: E.g. we want to publish which lock to take first to prevent an ABBA problem (extreme example): rcu_assign_pointer(lockptr, min(lptr1, lptr2)); Couldn't a compiler spill the lockptr memory location as a temporary buffer if the compiler is under register pressure? (yes, this seems unlikely if we flushed out most registers to memory because of the barrier, but still... ;) ) This seems to be also the case if we publish a multi-dereferencing pointers e.g. ptr->ptr->ptr. Thanks, Hannes -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
