X-Git-Url: https://bbs.cooldavid.org/git/?a=blobdiff_plain;f=fs%2Fnamei.c;h=11de7c39ff76efb5fed2e09f34f0ac212df58cf0;hb=b04f784e5d19ed58892833dae845738972cea260;hp=b815a4d2e1d6a326d1aefdcfb4ab5e919dd0de19;hpb=2a4419b5b2a77f3f4537c14f7ad7df95770655dd;p=net-next-2.6.git

diff --git a/fs/namei.c b/fs/namei.c
index b815a4d2e1d..11de7c39ff7 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -735,6 +735,11 @@ static int do_lookup(struct nameidata *nd, struct qstr *name,
 			return err;
 	}
 
+	/*
+	 * Rename seqlock is not required here because in the off chance
+	 * of a false negative due to a concurrent rename, we're going to
+	 * do the non-racy lookup, below.
+	 */
 	dentry = __d_lookup(nd->path.dentry, name);
 	if (!dentry)
 		goto need_lookup;
@@ -754,17 +759,13 @@ need_lookup:
 	mutex_lock(&dir->i_mutex);
 	/*
 	 * First re-do the cached lookup just in case it was created
-	 * while we waited for the directory semaphore..
-	 *
-	 * FIXME! This could use version numbering or similar to
-	 * avoid unnecessary cache lookups.
-	 *
-	 * The "dcache_lock" is purely to protect the RCU list walker
-	 * from concurrent renames at this point (we mustn't get false
-	 * negatives from the RCU list walk here, unlike the optimistic
-	 * fast walk).
+	 * while we waited for the directory semaphore, or the first
+	 * lookup failed due to an unrelated rename.
 	 *
-	 * so doing d_lookup() (with seqlock), instead of lockfree __d_lookup
+	 * This could use version numbering or similar to avoid unnecessary
+	 * cache lookups, but then we'd have to do the first lookup in the
+	 * non-racy way. However in the common case here, everything should
+	 * be hot in cache, so would it be a big win?
 	 */
 	dentry = d_lookup(parent, name);
 	if (likely(!dentry)) {
@@ -1136,13 +1137,12 @@ static struct dentry *__lookup_hash(struct qstr *name,
 			goto out;
 	}
 
-	dentry = __d_lookup(base, name);
-
-	/* lockess __d_lookup may fail due to concurrent d_move()
-	 * in some unrelated directory, so try with d_lookup
+	/*
+	 * Don't bother with __d_lookup: callers are for creat as
+	 * well as unlink, so a lot of the time it would cost
+	 * a double lookup.
 	 */
-	if (!dentry)
-		dentry = d_lookup(base, name);
+	dentry = d_lookup(base, name);
 
 	if (dentry && dentry->d_op && dentry->d_op->d_revalidate)
 		dentry = do_revalidate(dentry, nd);