On Fri, Apr 26, 2013 at 10:03:13AM +0200, Peter Zijlstra wrote: > On Fri, Apr 26, 2013 at 10:45:08AM +0900, Simon Horman wrote: > > > @@ -975,8 +975,7 @@ static void *ip_vs_conn_array(struct seq_file *seq, loff_t pos) > > return cp; > > } > > } > > - rcu_read_unlock(); > > - rcu_read_lock(); > > + cond_resched_rcu_lock(); > > } > > > While I agree with the sentiment I do find it a somewhat dangerous construct in > that it might become far too easy to keep an RCU reference over this break and > thus violate the RCU premise. > > Is there anything that can detect this? Sparse / cocinelle / smatch? If so it > would be great to add this to these checkers. I have done some crude coccinelle patterns in the past, but they are subject to false positives (from when you transfer the pointer from RCU protection to reference-count protection) and also false negatives (when you atomically increment some statistic unrelated to protection). I could imagine maintaining a per-thread count of the number of outermost RCU read-side critical sections at runtime, and then associating that counter with a given pointer at rcu_dereference() time, but this would require either compiler magic or an API for using a pointer returned by rcu_dereference(). This API could in theory be enforced by sparse. Dhaval Giani might have some ideas as well, adding him to CC. Thanx, Paul -- To unsubscribe from this list: send the line "unsubscribe netfilter-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
