locks: break delegations on link

Cc: Tyler Hicks <tyhicks@canonical.com>
Cc: Dustin Kirkland <dustin.kirkland@gazzang.com>
Acked-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

4 files changed, 35 insertions, 7 deletions

diff --git a/fs/ecryptfs/inode.c b/fs/ecryptfs/inode.c
index c23b01bb7e04..1c628f023041 100644
--- a/fs/ecryptfs/inode.c
+++ b/fs/ecryptfs/inode.c
@@ -475,7 +475,7 @@ static int ecryptfs_link(struct dentry *old_dentry, struct inode *dir,
         dget(lower_new_dentry);
         lower_dir_dentry = lock_parent(lower_new_dentry);
         rc = vfs_link(lower_old_dentry, lower_dir_dentry->d_inode,
-                      lower_new_dentry);
+                      lower_new_dentry, NULL);
         if (rc || !lower_new_dentry->d_inode)
                 goto out_lock;
         rc = ecryptfs_interpose(lower_new_dentry, new_dentry, dir->i_sb);
diff --git a/fs/namei.c b/fs/namei.c
index ce7e580e4e14..251178a1e383 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -3819,7 +3819,26 @@ SYSCALL_DEFINE2(symlink, const char __user *, oldname, const char __user *, newn
         return sys_symlinkat(oldname, AT_FDCWD, newname);
 }
 
-int vfs_link(struct dentry *old_dentry, struct inode *dir, struct dentry *new_dentry)
+/**
+ * vfs_link - create a new link
+ * @old_dentry: object to be linked
+ * @dir:        new parent
+ * @new_dentry: where to create the new link
+ * @delegated_inode: returns inode needing a delegation break
+ *
+ * The caller must hold dir->i_mutex
+ *
+ * If vfs_link discovers a delegation on the to-be-linked file in need
+ * of breaking, it will return -EWOULDBLOCK and return a reference to the
+ * inode in delegated_inode.  The caller should then break the delegation
+ * and retry.  Because breaking a delegation may take a long time, the
+ * caller should drop the i_mutex before doing so.
+ *
+ * Alternatively, a caller may pass NULL for delegated_inode.  This may
+ * be appropriate for callers that expect the underlying filesystem not
+ * to be NFS exported.
+ */
+int vfs_link(struct dentry *old_dentry, struct inode *dir, struct dentry *new_dentry, struct inode **delegated_inode)
 {
         struct inode *inode = old_dentry->d_inode;
         unsigned max_links = dir->i_sb->s_max_links;
@@ -3855,8 +3874,11 @@ int vfs_link(struct dentry *old_dentry, struct inode *dir, struct dentry *new_de
                 error =  -ENOENT;
         else if (max_links && inode->i_nlink >= max_links)
                 error = -EMLINK;
-        else
-                error = dir->i_op->link(old_dentry, dir, new_dentry);
+        else {
+                error = try_break_deleg(inode, delegated_inode);
+                if (!error)
+                        error = dir->i_op->link(old_dentry, dir, new_dentry);
+        }
 
         if (!error && (inode->i_state & I_LINKABLE)) {
                 spin_lock(&inode->i_lock);
@@ -3883,6 +3905,7 @@ SYSCALL_DEFINE5(linkat, int, olddfd, const char __user *, oldname,
 {
         struct dentry *new_dentry;
         struct path old_path, new_path;
+        struct inode *delegated_inode = NULL;
         int how = 0;
         int error;
 
@@ -3921,9 +3944,14 @@ retry:
         error = security_path_link(old_path.dentry, &new_path, new_dentry);
         if (error)
                 goto out_dput;
-        error = vfs_link(old_path.dentry, new_path.dentry->d_inode, new_dentry);
+        error = vfs_link(old_path.dentry, new_path.dentry->d_inode, new_dentry, &delegated_inode);
 out_dput:
         done_path_create(&new_path, new_dentry);
+        if (delegated_inode) {
+                error = break_deleg_wait(&delegated_inode);
+                if (!error)
+                        goto retry;
+        }
         if (retry_estale(error, how)) {
                 how |= LOOKUP_REVAL;
                 goto retry;
diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
index 45bf0295894d..27ba21b5f383 100644
--- a/fs/nfsd/vfs.c
+++ b/fs/nfsd/vfs.c
@@ -1736,7 +1736,7 @@ nfsd_link(struct svc_rqst *rqstp, struct svc_fh *ffhp,
                 err = nfserrno(host_err);
                 goto out_dput;
         }
-        host_err = vfs_link(dold, dirp, dnew);
+        host_err = vfs_link(dold, dirp, dnew, NULL);
         if (!host_err) {
                 err = nfserrno(commit_metadata(ffhp));
                 if (!err)
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 5bcff883fa90..6e36e7118ec1 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1453,7 +1453,7 @@ extern int vfs_create(struct inode *, struct dentry *, umode_t, bool);
 extern int vfs_mkdir(struct inode *, struct dentry *, umode_t);
 extern int vfs_mknod(struct inode *, struct dentry *, umode_t, dev_t);
 extern int vfs_symlink(struct inode *, struct dentry *, const char *);
-extern int vfs_link(struct dentry *, struct inode *, struct dentry *);
+extern int vfs_link(struct dentry *, struct inode *, struct dentry *, struct inode **);
 extern int vfs_rmdir(struct inode *, struct dentry *);
 extern int vfs_unlink(struct inode *, struct dentry *, struct inode **);
 extern int vfs_rename(struct inode *, struct dentry *, struct inode *, struct dentry *, struct inode **);