Re: [PATCH v2 1/4] dcache: Don't take unnecessary lock in d_count update

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On 04/05/2013 01:12 PM, Al Viro wrote:
@@ -635,22 +640,14 @@ struct dentry *dget_parent(struct dentry *dentry)
  {
  	struct dentry *ret;

-repeat:
-	/*
-	 * Don't need rcu_dereference because we re-check it was correct under
-	 * the lock.
-	 */
  	rcu_read_lock();
-	ret = dentry->d_parent;
-	spin_lock(&ret->d_lock);
-	if (unlikely(ret != dentry->d_parent)) {
-		spin_unlock(&ret->d_lock);
-		rcu_read_unlock();
-		goto repeat;
-	}
+	ret = rcu_dereference(dentry->d_parent);
  	rcu_read_unlock();
+	if (dcount_inc_cmpxchg(ret))
+		return ret;
+	spin_lock(&ret->d_lock);
And WTF is going to protect your "ret" from being freed just as you'd done
rcu_read_unlock()?

I think I had made a mistake here. I should move the rcu_read_unlock() down to before the return statement as well as after the spin_lock(). Thank for pointing this out. I will fix that in the next version. Anything else that needs to be fixed?

Regards,
Longman
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