fs: remove extra lookup in __lookup_hash

[net-next-2.6.git] / fs / namei.c

diff --git a/fs/namei.c b/fs/namei.c
index b815a4d2e1d6a326d1aefdcfb4ab5e919dd0de19..11de7c39ff76efb5fed2e09f34f0ac212df58cf0 100644 (file)
--- 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);