1 files changed, 55 insertions, 64 deletions

diff --git a/fs/namei.c b/fs/namei.c
index 17ea76bf2fbe..24896e833565 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -595,15 +595,16 @@ int follow_up(struct path *path)
 {
         struct vfsmount *parent;
         struct dentry *mountpoint;
-        spin_lock(&vfsmount_lock);
+
+        br_read_lock(vfsmount_lock);
         parent = path->mnt->mnt_parent;
         if (parent == path->mnt) {
-                spin_unlock(&vfsmount_lock);
+                br_read_unlock(vfsmount_lock);
                 return 0;
         }
         mntget(parent);
         mountpoint = dget(path->mnt->mnt_mountpoint);
-        spin_unlock(&vfsmount_lock);
+        br_read_unlock(vfsmount_lock);
         dput(path->dentry);
         path->dentry = mountpoint;
         mntput(path->mnt);
@@ -686,6 +687,35 @@ static __always_inline void follow_dotdot(struct nameidata *nd)
 }
 
 /*
+ * Allocate a dentry with name and parent, and perform a parent
+ * directory ->lookup on it. Returns the new dentry, or ERR_PTR
+ * on error. parent->d_inode->i_mutex must be held. d_lookup must
+ * have verified that no child exists while under i_mutex.
+ */
+static struct dentry *d_alloc_and_lookup(struct dentry *parent,
+                                struct qstr *name, struct nameidata *nd)
+{
+        struct inode *inode = parent->d_inode;
+        struct dentry *dentry;
+        struct dentry *old;
+
+        /* Don't create child dentry for a dead directory. */
+        if (unlikely(IS_DEADDIR(inode)))
+                return ERR_PTR(-ENOENT);
+
+        dentry = d_alloc(parent, name);
+        if (unlikely(!dentry))
+                return ERR_PTR(-ENOMEM);
+
+        old = inode->i_op->lookup(inode, dentry, nd);
+        if (unlikely(old)) {
+                dput(dentry);
+                dentry = old;
+        }
+        return dentry;
+}
+
+/*
  *  It's more convoluted than I'd like it to be, but... it's still fairly
  *  small and for now I'd prefer to have fast path as straight as possible.
  *  It _is_ time-critical.
@@ -706,9 +736,15 @@ 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;
+found:
         if (dentry->d_op && dentry->d_op->d_revalidate)
                 goto need_revalidate;
 done:
@@ -724,56 +760,28 @@ 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..
+         * while we waited for the directory semaphore, or the first
+         * lookup failed due to an unrelated rename.
          *
-         * 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).
-         *
-         * 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 (!dentry) {
-                struct dentry *new;
-
-                /* Don't create child dentry for a dead directory. */
-                dentry = ERR_PTR(-ENOENT);
-                if (IS_DEADDIR(dir))
-                        goto out_unlock;
-
-                new = d_alloc(parent, name);
-                dentry = ERR_PTR(-ENOMEM);
-                if (new) {
-                        dentry = dir->i_op->lookup(dir, new, nd);
-                        if (dentry)
-                                dput(new);
-                        else
-                                dentry = new;
-                }
-out_unlock:
+        if (likely(!dentry)) {
+                dentry = d_alloc_and_lookup(parent, name, nd);
                 mutex_unlock(&dir->i_mutex);
                 if (IS_ERR(dentry))
                         goto fail;
                 goto done;
         }
-
         /*
          * Uhhuh! Nasty case: the cache was re-populated while
          * we waited on the semaphore. Need to revalidate.
          */
         mutex_unlock(&dir->i_mutex);
-        if (dentry->d_op && dentry->d_op->d_revalidate) {
-                dentry = do_revalidate(dentry, nd);
-                if (!dentry)
-                        dentry = ERR_PTR(-ENOENT);
-        }
-        if (IS_ERR(dentry))
-                goto fail;
-        goto done;
+        goto found;
 
 need_revalidate:
         dentry = do_revalidate(dentry, nd);
@@ -1130,35 +1138,18 @@ 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);
 
-        if (!dentry) {
-                struct dentry *new;
-
-                /* Don't create child dentry for a dead directory. */
-                dentry = ERR_PTR(-ENOENT);
-                if (IS_DEADDIR(inode))
-                        goto out;
-
-                new = d_alloc(base, name);
-                dentry = ERR_PTR(-ENOMEM);
-                if (!new)
-                        goto out;
-                dentry = inode->i_op->lookup(inode, new, nd);
-                if (!dentry)
-                        dentry = new;
-                else
-                        dput(new);
-        }
+        if (!dentry)
+                dentry = d_alloc_and_lookup(base, name, nd);
 out:
         return dentry;
 }