1 files changed, 52 insertions, 66 deletions

diff --git a/fs/namei.c b/fs/namei.c
index e412421210cc..409a441ba2ae 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -494,50 +494,6 @@ static inline void unlock_rcu_walk(void)
 	br_read_unlock(&vfsmount_lock);
 }
 
-/*
- * When we move over from the RCU domain to properly refcounted
- * long-lived dentries, we need to check the sequence numbers
- * we got before lookup very carefully.
- *
- * We cannot blindly increment a dentry refcount - even if it
- * is not locked - if it is zero, because it may have gone
- * through the final d_kill() logic already.
- *
- * So for a zero refcount, we need to get the spinlock (which is
- * safe even for a dead dentry because the de-allocation is
- * RCU-delayed), and check the sequence count under the lock.
- *
- * Once we have checked the sequence count, we know it is live,
- * and since we hold the spinlock it cannot die from under us.
- *
- * In contrast, if the reference count wasn't zero, we can just
- * increment the lockref without having to take the spinlock.
- * Even if the sequence number ends up being stale, we haven't
- * gone through the final dput() and killed the dentry yet.
- */
-static inline int d_rcu_to_refcount(struct dentry *dentry, seqcount_t *validate, unsigned seq)
-{
-	int gotref;
-
-	gotref = lockref_get_or_lock(&dentry->d_lockref);
-
-	/* Does the sequence number still match? */
-	if (read_seqcount_retry(validate, seq)) {
-		if (gotref)
-			dput(dentry);
-		else
-			spin_unlock(&dentry->d_lock);
-		return -ECHILD;
-	}
-
-	/* Get the ref now, if we couldn't get it originally */
-	if (!gotref) {
-		dentry->d_lockref.count++;
-		spin_unlock(&dentry->d_lock);
-	}
-	return 0;
-}
-
 /**
  * unlazy_walk - try to switch to ref-walk mode.
  * @nd: nameidata pathwalk data
@@ -552,16 +508,29 @@ static int unlazy_walk(struct nameidata *nd, struct dentry *dentry)
 {
 	struct fs_struct *fs = current->fs;
 	struct dentry *parent = nd->path.dentry;
-	int want_root = 0;
 
 	BUG_ON(!(nd->flags & LOOKUP_RCU));
-	if (nd->root.mnt && !(nd->flags & LOOKUP_ROOT)) {
-		want_root = 1;
-		spin_lock(&fs->lock);
-		if (nd->root.mnt != fs->root.mnt ||
-				nd->root.dentry != fs->root.dentry)
-			goto err_root;
-	}
+
+	/*
+	 * Get a reference to the parent first: we're
+	 * going to make "path_put(nd->path)" valid in
+	 * non-RCU context for "terminate_walk()".
+	 *
+	 * If this doesn't work, return immediately with
+	 * RCU walking still active (and then we will do
+	 * the RCU walk cleanup in terminate_walk()).
+	 */
+	if (!lockref_get_not_dead(&parent->d_lockref))
+		return -ECHILD;
+
+	/*
+	 * After the mntget(), we terminate_walk() will do
+	 * the right thing for non-RCU mode, and all our
+	 * subsequent exit cases should unlock_rcu_walk()
+	 * before returning.
+	 */
+	mntget(nd->path.mnt);
+	nd->flags &= ~LOOKUP_RCU;
 
 	/*
 	 * For a negative lookup, the lookup sequence point is the parents
@@ -575,30 +544,42 @@ static int unlazy_walk(struct nameidata *nd, struct dentry *dentry)
 	 * be valid if the child sequence number is still valid.
 	 */
 	if (!dentry) {
-		if (d_rcu_to_refcount(parent, &parent->d_seq, nd->seq) < 0)
-			goto err_root;
+		if (read_seqcount_retry(&parent->d_seq, nd->seq))
+			goto out;
 		BUG_ON(nd->inode != parent->d_inode);
 	} else {
-		if (d_rcu_to_refcount(dentry, &dentry->d_seq, nd->seq) < 0)
-			goto err_root;
-		if (d_rcu_to_refcount(parent, &dentry->d_seq, nd->seq) < 0)
-			goto err_parent;
+		if (!lockref_get_not_dead(&dentry->d_lockref))
+			goto out;
+		if (read_seqcount_retry(&dentry->d_seq, nd->seq))
+			goto drop_dentry;
 	}
-	if (want_root) {
+
+	/*
+	 * Sequence counts matched. Now make sure that the root is
+	 * still valid and get it if required.
+	 */
+	if (nd->root.mnt && !(nd->flags & LOOKUP_ROOT)) {
+		spin_lock(&fs->lock);
+		if (nd->root.mnt != fs->root.mnt || nd->root.dentry != fs->root.dentry)
+			goto unlock_and_drop_dentry;
 		path_get(&nd->root);
 		spin_unlock(&fs->lock);
 	}
-	mntget(nd->path.mnt);
 
 	unlock_rcu_walk();
-	nd->flags &= ~LOOKUP_RCU;
 	return 0;
 
-err_parent:
+unlock_and_drop_dentry:
+	spin_unlock(&fs->lock);
+drop_dentry:
+	unlock_rcu_walk();
 	dput(dentry);
-err_root:
-	if (want_root)
-		spin_unlock(&fs->lock);
+	goto drop_root_mnt;
+out:
+	unlock_rcu_walk();
+drop_root_mnt:
+	if (!(nd->flags & LOOKUP_ROOT))
+		nd->root.mnt = NULL;
 	return -ECHILD;
 }
 
@@ -627,8 +608,13 @@ static int complete_walk(struct nameidata *nd)
 		if (!(nd->flags & LOOKUP_ROOT))
 			nd->root.mnt = NULL;
 
-		if (d_rcu_to_refcount(dentry, &dentry->d_seq, nd->seq) < 0) {
+		if (unlikely(!lockref_get_not_dead(&dentry->d_lockref))) {
+			unlock_rcu_walk();
+			return -ECHILD;
+		}
+		if (read_seqcount_retry(&dentry->d_seq, nd->seq)) {
 			unlock_rcu_walk();
+			dput(dentry);
 			return -ECHILD;
 		}
 		mntget(nd->path.mnt);