On 01/21, Paul E. McKenney wrote: > > On Fri, Jan 21, 2011 at 06:53:45PM +0100, Oleg Nesterov wrote: > > > > But rcu_dereference_raw() looks a bit confusing, and it is not > > very convenient to use read_barrier_depends() directly. > > > > Paul, may be it makes sense to add the new trivial helper which > > can be used instead? > > > > Yes, this is only cosmetic issue, I know ;) > > Cosmetic issues can be pretty important to the poor guy trying to read > the code. ;-) Agreed! > What keeps the structure that rcu_dereference_raw() returns a pointer > to from going away? It can't go away, current owns its ->perf_event_ctxp[] pointers. But the pointer can be installed at any time by sys_perf_event_open(). Currently the code does ctx = current->perf_event_ctxp[ctxn]; if (ctx) do_something(ctx); and in theory we need smp_read_barrier_depends() in between. > Best would be if a lockdep condition could be > constructed from the answer to this question and added to the appropriate > rcu_dereference() primitive. In this case the condition is "true", so we can use rcu_dereference_raw(). The only problem, it looks confusing. Especially because you actually need rcu_read_lock() if you look at not_current_task->perf_event_ctxp[]. Oleg. -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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