Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs

Pull vfs pile 3 (of many) from Al Viro:
 "Waiman's conversion of d_path() and bits related to it,
  kern_path_mountpoint(), several cleanups and fixes (exportfs
  one is -stable fodder, IMO).

  There definitely will be more...  ;-/"

* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs:
  split read_seqretry_or_unlock(), convert d_walk() to resulting primitives
  dcache: Translating dentry into pathname without taking rename_lock
  autofs4 - fix device ioctl mount lookup
  introduce kern_path_mountpoint()
  rename user_path_umountat() to user_path_mountpoint_at()
  take unlazy_walk() into umount_lookup_last()
  Kill indirect include of file.h from eventfd.h, use fdget() in cgroup.c
  prune_super(): sb->s_op is never NULL
  exportfs: don't assume that ->iterate() won't feed us too long entries
  afs: get rid of redundant ->d_name.len checks

8 files changed, 221 insertions, 167 deletions

diff --git a/fs/afs/dir.c b/fs/afs/dir.c
index 0b74d31..646337d 100644
--- a/fs/afs/dir.c
+++ b/fs/afs/dir.c
@@ -751,10 +751,6 @@ static int afs_mkdir(struct inode *dir, struct dentry *dentry, umode_t mode)
 	_enter("{%x:%u},{%s},%ho",
 	       dvnode->fid.vid, dvnode->fid.vnode, dentry->d_name.name, mode);
 
-	ret = -ENAMETOOLONG;
-	if (dentry->d_name.len >= AFSNAMEMAX)
-		goto error;
-
 	key = afs_request_key(dvnode->volume->cell);
 	if (IS_ERR(key)) {
 		ret = PTR_ERR(key);
@@ -816,10 +812,6 @@ static int afs_rmdir(struct inode *dir, struct dentry *dentry)
 	_enter("{%x:%u},{%s}",
 	       dvnode->fid.vid, dvnode->fid.vnode, dentry->d_name.name);
 
-	ret = -ENAMETOOLONG;
-	if (dentry->d_name.len >= AFSNAMEMAX)
-		goto error;
-
 	key = afs_request_key(dvnode->volume->cell);
 	if (IS_ERR(key)) {
 		ret = PTR_ERR(key);
@@ -936,10 +928,6 @@ static int afs_create(struct inode *dir, struct dentry *dentry, umode_t mode,
 	_enter("{%x:%u},{%s},%ho,",
 	       dvnode->fid.vid, dvnode->fid.vnode, dentry->d_name.name, mode);
 
-	ret = -ENAMETOOLONG;
-	if (dentry->d_name.len >= AFSNAMEMAX)
-		goto error;
-
 	key = afs_request_key(dvnode->volume->cell);
 	if (IS_ERR(key)) {
 		ret = PTR_ERR(key);
@@ -1005,10 +993,6 @@ static int afs_link(struct dentry *from, struct inode *dir,
 	       dvnode->fid.vid, dvnode->fid.vnode,
 	       dentry->d_name.name);
 
-	ret = -ENAMETOOLONG;
-	if (dentry->d_name.len >= AFSNAMEMAX)
-		goto error;
-
 	key = afs_request_key(dvnode->volume->cell);
 	if (IS_ERR(key)) {
 		ret = PTR_ERR(key);
@@ -1053,10 +1037,6 @@ static int afs_symlink(struct inode *dir, struct dentry *dentry,
 	       dvnode->fid.vid, dvnode->fid.vnode, dentry->d_name.name,
 	       content);
 
-	ret = -ENAMETOOLONG;
-	if (dentry->d_name.len >= AFSNAMEMAX)
-		goto error;
-
 	ret = -EINVAL;
 	if (strlen(content) >= AFSPATHMAX)
 		goto error;
@@ -1127,10 +1107,6 @@ static int afs_rename(struct inode *old_dir, struct dentry *old_dentry,
 	       new_dvnode->fid.vid, new_dvnode->fid.vnode,
 	       new_dentry->d_name.name);
 
-	ret = -ENAMETOOLONG;
-	if (new_dentry->d_name.len >= AFSNAMEMAX)
-		goto error;
-
 	key = afs_request_key(orig_dvnode->volume->cell);
 	if (IS_ERR(key)) {
 		ret = PTR_ERR(key);
diff --git a/fs/autofs4/dev-ioctl.c b/fs/autofs4/dev-ioctl.c
index 743c7c2..0f00da3 100644
--- a/fs/autofs4/dev-ioctl.c
+++ b/fs/autofs4/dev-ioctl.c
@@ -183,13 +183,14 @@ static int autofs_dev_ioctl_protosubver(struct file *fp,
 	return 0;
 }
 
+/* Find the topmost mount satisfying test() */
 static int find_autofs_mount(const char *pathname,
 			     struct path *res,
 			     int test(struct path *path, void *data),
 			     void *data)
 {
 	struct path path;
-	int err = kern_path(pathname, 0, &path);
+	int err = kern_path_mountpoint(AT_FDCWD, pathname, &path, 0);
 	if (err)
 		return err;
 	err = -ENOENT;
@@ -197,10 +198,9 @@ static int find_autofs_mount(const char *pathname,
 		if (path.dentry->d_sb->s_magic == AUTOFS_SUPER_MAGIC) {
 			if (test(&path, data)) {
 				path_get(&path);
-				if (!err) /* already found some */
-					path_put(res);
 				*res = path;
 				err = 0;
+				break;
 			}
 		}
 		if (!follow_up(&path))
@@ -486,12 +486,11 @@ static int autofs_dev_ioctl_askumount(struct file *fp,
  * mount if there is one or 0 if it isn't a mountpoint.
  *
  * If we aren't supplied with a file descriptor then we
- * lookup the nameidata of the path and check if it is the
- * root of a mount. If a type is given we are looking for
- * a particular autofs mount and if we don't find a match
- * we return fail. If the located nameidata path is the
- * root of a mount we return 1 along with the super magic
- * of the mount or 0 otherwise.
+ * lookup the path and check if it is the root of a mount.
+ * If a type is given we are looking for a particular autofs
+ * mount and if we don't find a match we return fail. If the
+ * located path is the root of a mount we return 1 along with
+ * the super magic of the mount or 0 otherwise.
  *
  * In both cases the the device number (as returned by
  * new_encode_dev()) is also returned.
@@ -519,9 +518,11 @@ static int autofs_dev_ioctl_ismountpoint(struct file *fp,
 
 	if (!fp || param->ioctlfd == -1) {
 		if (autofs_type_any(type))
-			err = kern_path(name, LOOKUP_FOLLOW, &path);
+			err = kern_path_mountpoint(AT_FDCWD,
+						   name, &path, LOOKUP_FOLLOW);
 		else
-			err = find_autofs_mount(name, &path, test_by_type, &type);
+			err = find_autofs_mount(name, &path,
+						test_by_type, &type);
 		if (err)
 			goto out;
 		devid = new_encode_dev(path.dentry->d_sb->s_dev);
diff --git a/fs/dcache.c b/fs/dcache.c
index ca8e9cd..4d9df3c 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -88,6 +88,35 @@ EXPORT_SYMBOL(rename_lock);
 
 static struct kmem_cache *dentry_cache __read_mostly;
 
+/**
+ * read_seqbegin_or_lock - begin a sequence number check or locking block
+ * lock: sequence lock
+ * seq : sequence number to be checked
+ *
+ * First try it once optimistically without taking the lock. If that fails,
+ * take the lock. The sequence number is also used as a marker for deciding
+ * whether to be a reader (even) or writer (odd).
+ * N.B. seq must be initialized to an even number to begin with.
+ */
+static inline void read_seqbegin_or_lock(seqlock_t *lock, int *seq)
+{
+	if (!(*seq & 1))	/* Even */
+		*seq = read_seqbegin(lock);
+	else			/* Odd */
+		write_seqlock(lock);
+}
+
+static inline int need_seqretry(seqlock_t *lock, int seq)
+{
+	return !(seq & 1) && read_seqretry(lock, seq);
+}
+
+static inline void done_seqretry(seqlock_t *lock, int seq)
+{
+	if (seq & 1)
+		write_sequnlock(lock);
+}
+
 /*
  * This is the single most critical data structure when it comes
  * to the dcache: the hashtable for lookups. Somebody should try
@@ -1012,7 +1041,7 @@ void shrink_dcache_for_umount(struct super_block *sb)
  * the parenthood after dropping the lock and check
  * that the sequence number still matches.
  */
-static struct dentry *try_to_ascend(struct dentry *old, int locked, unsigned seq)
+static struct dentry *try_to_ascend(struct dentry *old, unsigned seq)
 {
 	struct dentry *new = old->d_parent;
 
@@ -1026,7 +1055,7 @@ static struct dentry *try_to_ascend(struct dentry *old, int locked, unsigned seq
 	 */
 	if (new != old->d_parent ||
 		 (old->d_flags & DCACHE_DENTRY_KILLED) ||
-		 (!locked && read_seqretry(&rename_lock, seq))) {
+		 need_seqretry(&rename_lock, seq)) {
 		spin_unlock(&new->d_lock);
 		new = NULL;
 	}
@@ -1063,13 +1092,12 @@ static void d_walk(struct dentry *parent, void *data,
 {
 	struct dentry *this_parent;
 	struct list_head *next;
-	unsigned seq;
-	int locked = 0;
+	unsigned seq = 0;
 	enum d_walk_ret ret;
 	bool retry = true;
 
-	seq = read_seqbegin(&rename_lock);
 again:
+	read_seqbegin_or_lock(&rename_lock, &seq);
 	this_parent = parent;
 	spin_lock(&this_parent->d_lock);
 
@@ -1123,13 +1151,13 @@ resume:
 	 */
 	if (this_parent != parent) {
 		struct dentry *child = this_parent;
-		this_parent = try_to_ascend(this_parent, locked, seq);
+		this_parent = try_to_ascend(this_parent, seq);
 		if (!this_parent)
 			goto rename_retry;
 		next = child->d_u.d_child.next;
 		goto resume;
 	}
-	if (!locked && read_seqretry(&rename_lock, seq)) {
+	if (need_seqretry(&rename_lock, seq)) {
 		spin_unlock(&this_parent->d_lock);
 		goto rename_retry;
 	}
@@ -1138,17 +1166,13 @@ resume:
 
 out_unlock:
 	spin_unlock(&this_parent->d_lock);
-	if (locked)
-		write_sequnlock(&rename_lock);
+	done_seqretry(&rename_lock, seq);
 	return;
 
 rename_retry:
 	if (!retry)
 		return;
-	if (locked)
-		goto again;
-	locked = 1;
-	write_seqlock(&rename_lock);
+	seq = 1;
 	goto again;
 }
 
@@ -2647,9 +2671,39 @@ static int prepend(char **buffer, int *buflen, const char *str, int namelen)
 	return 0;
 }
 
+/**
+ * prepend_name - prepend a pathname in front of current buffer pointer
+ * buffer: buffer pointer
+ * buflen: allocated length of the buffer
+ * name:   name string and length qstr structure
+ *
+ * With RCU path tracing, it may race with d_move(). Use ACCESS_ONCE() to
+ * make sure that either the old or the new name pointer and length are
+ * fetched. However, there may be mismatch between length and pointer.
+ * The length cannot be trusted, we need to copy it byte-by-byte until
+ * the length is reached or a null byte is found. It also prepends "/" at
+ * the beginning of the name. The sequence number check at the caller will
+ * retry it again when a d_move() does happen. So any garbage in the buffer
+ * due to mismatched pointer and length will be discarded.
+ */
 static int prepend_name(char **buffer, int *buflen, struct qstr *name)
 {
-	return prepend(buffer, buflen, name->name, name->len);
+	const char *dname = ACCESS_ONCE(name->name);
+	u32 dlen = ACCESS_ONCE(name->len);
+	char *p;
+
+	if (*buflen < dlen + 1)
+		return -ENAMETOOLONG;
+	*buflen -= dlen + 1;
+	p = *buffer -= dlen + 1;
+	*p++ = '/';
+	while (dlen--) {
+		char c = *dname++;
+		if (!c)
+			break;
+		*p++ = c;
+	}
+	return 0;
 }
 
 /**
@@ -2659,7 +2713,14 @@ static int prepend_name(char **buffer, int *buflen, struct qstr *name)
  * @buffer: pointer to the end of the buffer
  * @buflen: pointer to buffer length
  *
- * Caller holds the rename_lock.
+ * The function tries to write out the pathname without taking any lock other
+ * than the RCU read lock to make sure that dentries won't go away. It only
+ * checks the sequence number of the global rename_lock as any change in the
+ * dentry's d_seq will be preceded by changes in the rename_lock sequence
+ * number. If the sequence number had been change, it will restart the whole
+ * pathname back-tracing sequence again. It performs a total of 3 trials of
+ * lockless back-tracing sequences before falling back to take the
+ * rename_lock.
  */
 static int prepend_path(const struct path *path,
 			const struct path *root,
@@ -2668,54 +2729,66 @@ static int prepend_path(const struct path *path,
 	struct dentry *dentry = path->dentry;
 	struct vfsmount *vfsmnt = path->mnt;
 	struct mount *mnt = real_mount(vfsmnt);
-	bool slash = false;
 	int error = 0;
+	unsigned seq = 0;
+	char *bptr;
+	int blen;
 
+	rcu_read_lock();
+restart:
+	bptr = *buffer;
+	blen = *buflen;
+	read_seqbegin_or_lock(&rename_lock, &seq);
 	while (dentry != root->dentry || vfsmnt != root->mnt) {
 		struct dentry * parent;
 
 		if (dentry == vfsmnt->mnt_root || IS_ROOT(dentry)) {
 			/* Global root? */
-			if (!mnt_has_parent(mnt))
-				goto global_root;
-			dentry = mnt->mnt_mountpoint;
-			mnt = mnt->mnt_parent;
-			vfsmnt = &mnt->mnt;
-			continue;
+			if (mnt_has_parent(mnt)) {
+				dentry = mnt->mnt_mountpoint;
+				mnt = mnt->mnt_parent;
+				vfsmnt = &mnt->mnt;
+				continue;
+			}
+			/*
+			 * Filesystems needing to implement special "root names"
+			 * should do so with ->d_dname()
+			 */
+			if (IS_ROOT(dentry) &&
+			   (dentry->d_name.len != 1 ||
+			    dentry->d_name.name[0] != '/')) {
+				WARN(1, "Root dentry has weird name <%.*s>\n",
+				     (int) dentry->d_name.len,
+				     dentry->d_name.name);
+			}
+			if (!error)
+				error = is_mounted(vfsmnt) ? 1 : 2;
+			break;
 		}
 		parent = dentry->d_parent;
 		prefetch(parent);
-		spin_lock(&dentry->d_lock);
-		error = prepend_name(buffer, buflen, &dentry->d_name);
-		spin_unlock(&dentry->d_lock);
-		if (!error)
-			error = prepend(buffer, buflen, "/", 1);
+		error = prepend_name(&bptr, &blen, &dentry->d_name);
 		if (error)
 			break;
 
-		slash = true;
 		dentry = parent;
 	}
+	if (!(seq & 1))
+		rcu_read_unlock();
+	if (need_seqretry(&rename_lock, seq)) {
+		seq = 1;
+		goto restart;
+	}
+	done_seqretry(&rename_lock, seq);
 
-	if (!error && !slash)
-		error = prepend(buffer, buflen, "/", 1);
-
-	return error;
-
-global_root:
-	/*
-	 * Filesystems needing to implement special "root names"
-	 * should do so with ->d_dname()
-	 */
-	if (IS_ROOT(dentry) &&
-	    (dentry->d_name.len != 1 || dentry->d_name.name[0] != '/')) {
-		WARN(1, "Root dentry has weird name <%.*s>\n",
-		     (int) dentry->d_name.len, dentry->d_name.name);
-	}
-	if (!slash)
-		error = prepend(buffer, buflen, "/", 1);
-	if (!error)
-		error = is_mounted(vfsmnt) ? 1 : 2;
+	if (error >= 0 && bptr == *buffer) {
+		if (--blen < 0)
+			error = -ENAMETOOLONG;
+		else
+			*--bptr = '/';
+	}
+	*buffer = bptr;
+	*buflen = blen;
 	return error;
 }
 
@@ -2744,9 +2817,7 @@ char *__d_path(const struct path *path,
 
 	prepend(&res, &buflen, "\0", 1);
 	br_read_lock(&vfsmount_lock);
-	write_seqlock(&rename_lock);
 	error = prepend_path(path, root, &res, &buflen);
-	write_sequnlock(&rename_lock);
 	br_read_unlock(&vfsmount_lock);
 
 	if (error < 0)
@@ -2765,9 +2836,7 @@ char *d_absolute_path(const struct path *path,
 
 	prepend(&res, &buflen, "\0", 1);
 	br_read_lock(&vfsmount_lock);
-	write_seqlock(&rename_lock);
 	error = prepend_path(path, &root, &res, &buflen);
-	write_sequnlock(&rename_lock);
 	br_read_unlock(&vfsmount_lock);
 
 	if (error > 1)
@@ -2833,9 +2902,7 @@ char *d_path(const struct path *path, char *buf, int buflen)
 
 	get_fs_root(current->fs, &root);
 	br_read_lock(&vfsmount_lock);
-	write_seqlock(&rename_lock);
 	error = path_with_deleted(path, &root, &res, &buflen);
-	write_sequnlock(&rename_lock);
 	br_read_unlock(&vfsmount_lock);
 	if (error < 0)
 		res = ERR_PTR(error);
@@ -2870,10 +2937,10 @@ char *simple_dname(struct dentry *dentry, char *buffer, int buflen)
 	char *end = buffer + buflen;
 	/* these dentries are never renamed, so d_lock is not needed */
 	if (prepend(&end, &buflen, " (deleted)", 11) ||
-	    prepend_name(&end, &buflen, &dentry->d_name) ||
+	    prepend(&end, &buflen, dentry->d_name.name, dentry->d_name.len) ||
 	    prepend(&end, &buflen, "/", 1))  
 		end = ERR_PTR(-ENAMETOOLONG);
-	return end;  
+	return end;
 }
 
 /*
@@ -2881,30 +2948,42 @@ char *simple_dname(struct dentry *dentry, char *buffer, int buflen)
  */
 static char *__dentry_path(struct dentry *dentry, char *buf, int buflen)
 {
-	char *end = buf + buflen;
-	char *retval;
+	char *end, *retval;
+	int len, seq = 0;
+	int error = 0;
 
-	prepend(&end, &buflen, "\0", 1);
+	rcu_read_lock();
+restart:
+	end = buf + buflen;
+	len = buflen;
+	prepend(&end, &len, "\0", 1);
 	if (buflen < 1)
 		goto Elong;
 	/* Get '/' right */
 	retval = end-1;
 	*retval = '/';
-
+	read_seqbegin_or_lock(&rename_lock, &seq);
 	while (!IS_ROOT(dentry)) {
 		struct dentry *parent = dentry->d_parent;
 		int error;
 
 		prefetch(parent);
-		spin_lock(&dentry->d_lock);
-		error = prepend_name(&end, &buflen, &dentry->d_name);
-		spin_unlock(&dentry->d_lock);
-		if (error != 0 || prepend(&end, &buflen, "/", 1) != 0)
-			goto Elong;
+		error = prepend_name(&end, &len, &dentry->d_name);
+		if (error)
+			break;
 
 		retval = end;
 		dentry = parent;
 	}
+	if (!(seq & 1))
+		rcu_read_unlock();
+	if (need_seqretry(&rename_lock, seq)) {
+		seq = 1;
+		goto restart;
+	}
+	done_seqretry(&rename_lock, seq);
+	if (error)
+		goto Elong;
 	return retval;
 Elong:
 	return ERR_PTR(-ENAMETOOLONG);
@@ -2912,13 +2991,7 @@ Elong:
 
 char *dentry_path_raw(struct dentry *dentry, char *buf, int buflen)
 {
-	char *retval;
-
-	write_seqlock(&rename_lock);
-	retval = __dentry_path(dentry, buf, buflen);
-	write_sequnlock(&rename_lock);
-
-	return retval;
+	return __dentry_path(dentry, buf, buflen);
 }
 EXPORT_SYMBOL(dentry_path_raw);
 
@@ -2927,7 +3000,6 @@ char *dentry_path(struct dentry *dentry, char *buf, int buflen)
 	char *p = NULL;
 	char *retval;
 
-	write_seqlock(&rename_lock);
 	if (d_unlinked(dentry)) {
 		p = buf + buflen;
 		if (prepend(&p, &buflen, "//deleted", 10) != 0)
@@ -2935,7 +3007,6 @@ char *dentry_path(struct dentry *dentry, char *buf, int buflen)
 		buflen++;
 	}
 	retval = __dentry_path(dentry, buf, buflen);
-	write_sequnlock(&rename_lock);
 	if (!IS_ERR(retval) && p)
 		*p = '/';	/* restore '/' overriden with '\0' */
 	return retval;
@@ -2974,7 +3045,6 @@ SYSCALL_DEFINE2(getcwd, char __user *, buf, unsigned long, size)
 
 	error = -ENOENT;
 	br_read_lock(&vfsmount_lock);
-	write_seqlock(&rename_lock);
 	if (!d_unlinked(pwd.dentry)) {
 		unsigned long len;
 		char *cwd = page + PAGE_SIZE;
@@ -2982,7 +3052,6 @@ SYSCALL_DEFINE2(getcwd, char __user *, buf, unsigned long, size)
 
 		prepend(&cwd, &buflen, "\0", 1);
 		error = prepend_path(&pwd, &root, &cwd, &buflen);
-		write_sequnlock(&rename_lock);
 		br_read_unlock(&vfsmount_lock);
 
 		if (error < 0)
@@ -3003,7 +3072,6 @@ SYSCALL_DEFINE2(getcwd, char __user *, buf, unsigned long, size)
 				error = -EFAULT;
 		}
 	} else {
-		write_sequnlock(&rename_lock);
 		br_read_unlock(&vfsmount_lock);
 	}
 
diff --git a/fs/exportfs/expfs.c b/fs/exportfs/expfs.c
index 293bc2e..a235f00 100644
--- a/fs/exportfs/expfs.c
+++ b/fs/exportfs/expfs.c
@@ -231,7 +231,7 @@ static int filldir_one(void * __buf, const char * name, int len,
 	int result = 0;
 
 	buf->sequence++;
-	if (buf->ino == ino) {
+	if (buf->ino == ino && len <= NAME_MAX) {
 		memcpy(buf->name, name, len);
 		buf->name[len] = '\0';
 		buf->found = 1;
diff --git a/fs/internal.h b/fs/internal.h
index d208937..2be46ea 100644
--- a/fs/internal.h
+++ b/fs/internal.h
@@ -45,6 +45,9 @@ extern void __init chrdev_init(void);
  * namei.c
  */
 extern int __inode_permission(struct inode *, int);
+extern int user_path_mountpoint_at(int, const char __user *, unsigned int, struct path *);
+extern int vfs_path_lookup(struct dentry *, struct vfsmount *,
+			   const char *, unsigned int, struct path *);
 
 /*
  * namespace.c
diff --git a/fs/namei.c b/fs/namei.c
index 5e6aaad..409a441 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -2209,7 +2209,7 @@ user_path_parent(int dfd, const char __user *path, struct nameidata *nd,
 }
 
 /**
- * umount_lookup_last - look up last component for umount
+ * mountpoint_last - look up last component for umount
  * @nd:   pathwalk nameidata - currently pointing at parent directory of "last"
  * @path: pointer to container for result
  *
@@ -2236,25 +2236,28 @@ user_path_parent(int dfd, const char __user *path, struct nameidata *nd,
  *         to the link, and nd->path will *not* be put.
  */
 static int
-umount_lookup_last(struct nameidata *nd, struct path *path)
+mountpoint_last(struct nameidata *nd, struct path *path)
 {
 	int error = 0;
 	struct dentry *dentry;
 	struct dentry *dir = nd->path.dentry;
 
-	if (unlikely(nd->flags & LOOKUP_RCU)) {
-		WARN_ON_ONCE(1);
-		error = -ECHILD;
-		goto error_check;
+	/* If we're in rcuwalk, drop out of it to handle last component */
+	if (nd->flags & LOOKUP_RCU) {
+		if (unlazy_walk(nd, NULL)) {
+			error = -ECHILD;
+			goto out;
+		}
 	}
 
 	nd->flags &= ~LOOKUP_PARENT;
 
 	if (unlikely(nd->last_type != LAST_NORM)) {
 		error = handle_dots(nd, nd->last_type);
-		if (!error)
-			dentry = dget(nd->path.dentry);
-		goto error_check;
+		if (error)
+			goto out;
+		dentry = dget(nd->path.dentry);
+		goto done;
 	}
 
 	mutex_lock(&dir->d_inode->i_mutex);
@@ -2268,44 +2271,43 @@ umount_lookup_last(struct nameidata *nd, struct path *path)
 		dentry = d_alloc(dir, &nd->last);
 		if (!dentry) {
 			error = -ENOMEM;
-		} else {
-			dentry = lookup_real(dir->d_inode, dentry, nd->flags);
-			if (IS_ERR(dentry))
-				error = PTR_ERR(dentry);
+			goto out;
 		}
+		dentry = lookup_real(dir->d_inode, dentry, nd->flags);
+		error = PTR_ERR(dentry);
+		if (IS_ERR(dentry))
+			goto out;
 	}
 	mutex_unlock(&dir->d_inode->i_mutex);
 
-error_check:
-	if (!error) {
-		if (!dentry->d_inode) {
-			error = -ENOENT;
-			dput(dentry);
-		} else {
-			path->dentry = dentry;
-			path->mnt = mntget(nd->path.mnt);
-			if (should_follow_link(dentry->d_inode,
-						nd->flags & LOOKUP_FOLLOW))
-				return 1;
-			follow_mount(path);
-		}
+done:
+	if (!dentry->d_inode) {
+		error = -ENOENT;
+		dput(dentry);
+		goto out;
 	}
+	path->dentry = dentry;
+	path->mnt = mntget(nd->path.mnt);
+	if (should_follow_link(dentry->d_inode, nd->flags & LOOKUP_FOLLOW))
+		return 1;
+	follow_mount(path);
+	error = 0;
+out:
 	terminate_walk(nd);
 	return error;
 }
 
 /**
- * path_umountat - look up a path to be umounted
+ * path_mountpoint - look up a path to be umounted
  * @dfd:	directory file descriptor to start walk from
  * @name:	full pathname to walk
  * @flags:	lookup flags
- * @nd:		pathwalk nameidata
  *
  * Look up the given name, but don't attempt to revalidate the last component.
  * Returns 0 and "path" will be valid on success; Retuns error otherwise.
  */
 static int
-path_umountat(int dfd, const char *name, struct path *path, unsigned int flags)
+path_mountpoint(int dfd, const char *name, struct path *path, unsigned int flags)
 {
 	struct file *base = NULL;
 	struct nameidata nd;
@@ -2320,16 +2322,7 @@ path_umountat(int dfd, const char *name, struct path *path, unsigned int flags)
 	if (err)
 		goto out;
 
-	/* If we're in rcuwalk, drop out of it to handle last component */
-	if (nd.flags & LOOKUP_RCU) {
-		err = unlazy_walk(&nd, NULL);
-		if (err) {
-			terminate_walk(&nd);
-			goto out;
-		}
-	}
-
-	err = umount_lookup_last(&nd, path);
+	err = mountpoint_last(&nd, path);
 	while (err > 0) {
 		void *cookie;
 		struct path link = *path;
@@ -2340,7 +2333,7 @@ path_umountat(int dfd, const char *name, struct path *path, unsigned int flags)
 		err = follow_link(&link, &nd, &cookie);
 		if (err)
 			break;
-		err = umount_lookup_last(&nd, path);
+		err = mountpoint_last(&nd, path);
 		put_link(&nd, &link, cookie);
 	}
 out:
@@ -2353,8 +2346,22 @@ out:
 	return err;
 }
 
+static int
+filename_mountpoint(int dfd, struct filename *s, struct path *path,
+			unsigned int flags)
+{
+	int error = path_mountpoint(dfd, s->name, path, flags | LOOKUP_RCU);
+	if (unlikely(error == -ECHILD))
+		error = path_mountpoint(dfd, s->name, path, flags);
+	if (unlikely(error == -ESTALE))
+		error = path_mountpoint(dfd, s->name, path, flags | LOOKUP_REVAL);
+	if (likely(!error))
+		audit_inode(s, path->dentry, 0);
+	return error;
+}
+
 /**
- * user_path_umountat - lookup a path from userland in order to umount it
+ * user_path_mountpoint_at - lookup a path from userland in order to umount it
  * @dfd:	directory file descriptor
  * @name:	pathname from userland
  * @flags:	lookup flags
@@ -2368,28 +2375,27 @@ out:
  * Returns 0 and populates "path" on success.
  */
 int
-user_path_umountat(int dfd, const char __user *name, unsigned int flags,
+user_path_mountpoint_at(int dfd, const char __user *name, unsigned int flags,
 			struct path *path)
 {
 	struct filename *s = getname(name);
 	int error;
-
 	if (IS_ERR(s))
 		return PTR_ERR(s);
-
-	error = path_umountat(dfd, s->name, path, flags | LOOKUP_RCU);
-	if (unlikely(error == -ECHILD))
-		error = path_umountat(dfd, s->name, path, flags);
-	if (unlikely(error == -ESTALE))
-		error = path_umountat(dfd, s->name, path, flags | LOOKUP_REVAL);
-
-	if (likely(!error))
-		audit_inode(s, path->dentry, 0);
-
+	error = filename_mountpoint(dfd, s, path, flags);
 	putname(s);
 	return error;
 }
 
+int
+kern_path_mountpoint(int dfd, const char *name, struct path *path,
+			unsigned int flags)
+{
+	struct filename s = {.name = name};
+	return filename_mountpoint(dfd, &s, path, flags);
+}
+EXPORT_SYMBOL(kern_path_mountpoint);
+
 /*
  * It's inline, so penalty for filesystems that don't use sticky bit is
  * minimal.
diff --git a/fs/namespace.c b/fs/namespace.c
index fc2b522..25845d1 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1321,7 +1321,7 @@ SYSCALL_DEFINE2(umount, char __user *, name, int, flags)
 	if (!(flags & UMOUNT_NOFOLLOW))
 		lookup_flags |= LOOKUP_FOLLOW;
 
-	retval = user_path_umountat(AT_FDCWD, name, lookup_flags, &path);
+	retval = user_path_mountpoint_at(AT_FDCWD, name, lookup_flags, &path);
 	if (retval)
 		goto out;
 	mnt = real_mount(path.mnt);
diff --git a/fs/super.c b/fs/super.c
index 5536a95..f6961ea 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -71,7 +71,7 @@ static int prune_super(struct shrinker *shrink, struct shrink_control *sc)
 	if (!grab_super_passive(sb))
 		return -1;
 
-	if (sb->s_op && sb->s_op->nr_cached_objects)
+	if (sb->s_op->nr_cached_objects)
 		fs_objects = sb->s_op->nr_cached_objects(sb);
 
 	total_objects = sb->s_nr_dentry_unused +