On Sat, Sep 25, 2010 at 10:55:20PM +0200, Rafael J. Wysocki wrote:dev_opp as discussed before is safe as it is never freed (find_device_opp uses it's own rcu_read_lock, the rcu_read_lock in this context is for the opp list. what am I missing?On Friday, September 24, 2010, Paul E. McKenney wrote:On Fri, Sep 24, 2010 at 07:50:40AM -0500, Nishanth Menon wrote:...Looks like a good start!!! Some questions and suggestions about RCU...
usage interspersed below.
However, it looks like it should run rcu_read_lock() before calling+ * Locking: RCU reader.This one is OK as well. You are returning a count, so if all of the
+ */
+int opp_get_opp_count(struct device *dev)
+{
+ struct device_opp *dev_opp;
+ struct opp *temp_opp;
+ int count = 0;
+
+ dev_opp = find_device_opp(dev);
+ if (IS_ERR(dev_opp))
+ return PTR_ERR(dev_opp);
+
+ rcu_read_lock();
+ list_for_each_entry_rcu(temp_opp, &dev_opp->opp_list, node) {
+ if (temp_opp->available)
+ count++;
+ }
+ rcu_read_unlock();
counted structures are freed at this point, no problem. The count was
valid when it was accumulated, and the fact that it might now be obsolete
is (usually) not a problem.
find_device_opp(dev), shouldn't it?
Indeed it does appear that you are right -- good catch!!!
Thanx, Paul