diff --git a/fs/namei.c b/fs/namei.c
index 45c702edce3c06b5bc245917770c145209defdfa..1067f7a0287ab105a30fbbcb353af74b4d8f9eb2 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -2272,6 +2272,8 @@ EXPORT_SYMBOL(vfs_path_lookup);
  *
  * Note that this routine is purely a helper for filesystem usage and should
  * not be called by generic code.
+ *
+ * The caller must hold base->i_mutex.
  */
 struct dentry *lookup_one_len(const char *name, struct dentry *base, int len)
 {
@@ -2315,6 +2317,75 @@ struct dentry *lookup_one_len(const char *name, struct dentry *base, int len)
 }
 EXPORT_SYMBOL(lookup_one_len);
 
+/**
+ * lookup_one_len_unlocked - filesystem helper to lookup single pathname component
+ * @name:	pathname component to lookup
+ * @base:	base directory to lookup from
+ * @len:	maximum length @len should be interpreted to
+ *
+ * Note that this routine is purely a helper for filesystem usage and should
+ * not be called by generic code.
+ *
+ * Unlike lookup_one_len, it should be called without the parent
+ * i_mutex held, and will take the i_mutex itself if necessary.
+ */
+struct dentry *lookup_one_len_unlocked(const char *name,
+				       struct dentry *base, int len)
+{
+	struct qstr this;
+	unsigned int c;
+	int err;
+	struct dentry *ret;
+
+	this.name = name;
+	this.len = len;
+	this.hash = full_name_hash(name, len);
+	if (!len)
+		return ERR_PTR(-EACCES);
+
+	if (unlikely(name[0] == '.')) {
+		if (len < 2 || (len == 2 && name[1] == '.'))
+			return ERR_PTR(-EACCES);
+	}
+
+	while (len--) {
+		c = *(const unsigned char *)name++;
+		if (c == '/' || c == '\0')
+			return ERR_PTR(-EACCES);
+	}
+	/*
+	 * See if the low-level filesystem might want
+	 * to use its own hash..
+	 */
+	if (base->d_flags & DCACHE_OP_HASH) {
+		int err = base->d_op->d_hash(base, &this);
+		if (err < 0)
+			return ERR_PTR(err);
+	}
+
+	err = inode_permission(base->d_inode, MAY_EXEC);
+	if (err)
+		return ERR_PTR(err);
+
+	/*
+	 * __d_lookup() is used to try to get a quick answer and avoid the
+	 * mutex.  A false-negative does no harm.
+	 */
+	ret = __d_lookup(base, &this);
+	if (ret && unlikely(ret->d_flags & DCACHE_OP_REVALIDATE)) {
+		dput(ret);
+		ret = NULL;
+	}
+	if (ret)
+		return ret;
+
+	mutex_lock(&base->d_inode->i_mutex);
+	ret =  __lookup_hash(&this, base, 0);
+	mutex_unlock(&base->d_inode->i_mutex);
+	return ret;
+}
+EXPORT_SYMBOL(lookup_one_len_unlocked);
+
 int user_path_at_empty(int dfd, const char __user *name, unsigned flags,
 		 struct path *path, int *empty)
 {
diff --git a/fs/nfsd/nfs3xdr.c b/fs/nfsd/nfs3xdr.c
index 00575d776d91f58576523d1fc30e558585a91ace..2246454dec7654b3570f3c52bb5264567e32064c 100644
--- a/fs/nfsd/nfs3xdr.c
+++ b/fs/nfsd/nfs3xdr.c
@@ -823,7 +823,7 @@ compose_entry_fh(struct nfsd3_readdirres *cd, struct svc_fh *fhp,
 		} else
 			dchild = dget(dparent);
 	} else
-		dchild = lookup_one_len(name, dparent, namlen);
+		dchild = lookup_one_len_unlocked(name, dparent, namlen);
 	if (IS_ERR(dchild))
 		return rv;
 	if (d_mountpoint(dchild))
diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c
index 51c9e9ca39a4d7c5e0537a2cafed4ec9caeb789d..325521ce389adb48d6d2e38c6e04375f363ecea4 100644
--- a/fs/nfsd/nfs4xdr.c
+++ b/fs/nfsd/nfs4xdr.c
@@ -2838,14 +2838,14 @@ nfsd4_encode_dirent_fattr(struct xdr_stream *xdr, struct nfsd4_readdir *cd,
 	__be32 nfserr;
 	int ignore_crossmnt = 0;
 
-	dentry = lookup_one_len(name, cd->rd_fhp->fh_dentry, namlen);
+	dentry = lookup_one_len_unlocked(name, cd->rd_fhp->fh_dentry, namlen);
 	if (IS_ERR(dentry))
 		return nfserrno(PTR_ERR(dentry));
 	if (d_really_is_negative(dentry)) {
 		/*
-		 * nfsd_buffered_readdir drops the i_mutex between
-		 * readdir and calling this callback, leaving a window
-		 * where this directory entry could have gone away.
+		 * we're not holding the i_mutex here, so there's
+		 * a window where this directory entry could have gone
+		 * away.
 		 */
 		dput(dentry);
 		return nfserr_noent;
diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
index 994d66fbb4467ac8892a4d2ae0e5e9fda2a05722..4212aaacbb5537610c7fa37aea478ed2b5216390 100644
--- a/fs/nfsd/vfs.c
+++ b/fs/nfsd/vfs.c
@@ -217,10 +217,16 @@ nfsd_lookup_dentry(struct svc_rqst *rqstp, struct svc_fh *fhp,
 		host_err = PTR_ERR(dentry);
 		if (IS_ERR(dentry))
 			goto out_nfserr;
-		/*
-		 * check if we have crossed a mount point ...
-		 */
 		if (nfsd_mountpoint(dentry, exp)) {
+			/*
+			 * We don't need the i_mutex after all.  It's
+			 * still possible we could open this (regular
+			 * files can be mountpoints too), but the
+			 * i_mutex is just there to prevent renames of
+			 * something that we might be about to delegate,
+			 * and a mountpoint won't be renamed:
+			 */
+			fh_unlock(fhp);
 			if ((host_err = nfsd_cross_mnt(rqstp, &dentry, &exp))) {
 				dput(dentry);
 				goto out_nfserr;
@@ -1809,7 +1815,6 @@ static __be32 nfsd_buffered_readdir(struct file *file, nfsd_filldir_t func,
 	offset = *offsetp;
 
 	while (1) {
-		struct inode *dir_inode = file_inode(file);
 		unsigned int reclen;
 
 		cdp->err = nfserr_eof; /* will be cleared on successful read */
@@ -1828,15 +1833,6 @@ static __be32 nfsd_buffered_readdir(struct file *file, nfsd_filldir_t func,
 		if (!size)
 			break;
 
-		/*
-		 * Various filldir functions may end up calling back into
-		 * lookup_one_len() and the file system's ->lookup() method.
-		 * These expect i_mutex to be held, as it would within readdir.
-		 */
-		host_err = mutex_lock_killable(&dir_inode->i_mutex);
-		if (host_err)
-			break;
-
 		de = (struct buffered_dirent *)buf.dirent;
 		while (size > 0) {
 			offset = de->offset;
@@ -1853,7 +1849,6 @@ static __be32 nfsd_buffered_readdir(struct file *file, nfsd_filldir_t func,
 			size -= reclen;
 			de = (struct buffered_dirent *)((char *)de + reclen);
 		}
-		mutex_unlock(&dir_inode->i_mutex);
 		if (size > 0) /* We bailed out early */
 			break;
 
diff --git a/include/linux/namei.h b/include/linux/namei.h
index d8c6334cd15005c16162f57959e20b2e09f99d03..d0f25d81b46a6c2f488c34e2cd14e91c49fb8145 100644
--- a/include/linux/namei.h
+++ b/include/linux/namei.h
@@ -77,6 +77,7 @@ extern struct dentry *kern_path_locked(const char *, struct path *);
 extern int kern_path_mountpoint(int, const char *, struct path *, unsigned int);
 
 extern struct dentry *lookup_one_len(const char *, struct dentry *, int);
+extern struct dentry *lookup_one_len_unlocked(const char *, struct dentry *, int);
 
 extern int follow_down_one(struct path *);
 extern int follow_down(struct path *);