Dmitry Torokhov a écrit : > On Thursday 19 March 2009 20:20:32 Arjan van de Ven wrote: >>> I don't claim to understand the code in question, so it is entirely >>> possible that the following is irrelevant. But one other reason for >>> synchronize_rcu() is: >>> >>> 1. Make change. >>> >>> 2. synchronize_rcu() >>> >>> 3. Now you are guaranteed that all CPUs/tasks/whatever >>> currently running either are not messing with you on the one hand, or >>> have seen the change on the other. >> ok so this is for the case where someone is already iterating the list. >> >> I don't see anything in the code that assumes this.. > > This is something that input core guarantees to its users: by the time > input core calls hander->start() or, in its absence, by the time > input_register_handle() returns, events from input drivers will be > passed into the handle being registered, i.e. the presence of the > new item in the list is noticed by all CPUs. > > Now, it is possible to stop using RCU primitives in the input core > but I think that you'd want to figure out why synchronize_rcu() > takes so long first, otheriwse you may find another "abuser" > down the road. > If a cpu does a loop, it nearly impossible that synchronize_rcu() can be fast. We had same problem in ksoftirqd(), where I had to add a call to rcu_qsctr_inc() to unblock other threads blocked in synchronize_rcu() http://git2.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=64ca5ab913f1594ef316556e65f5eae63ff50cee If a driver does a loop with no call to scheduler, it might have same problem -- To unsubscribe from this list: send the line "unsubscribe linux-input" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
