cifs - check S_AUTOMOUNT in revalidate

When revalidating a dentry, if the inode wasn't known to be a dfs
entry when the dentry was instantiated, such as when created via
->readdir(), the DCACHE_NEED_AUTOMOUNT flag needs to be set on the
dentry in ->d_revalidate().

The false return from cifs_d_revalidate(), due to the inode now
being marked with the S_AUTOMOUNT flag, might not invalidate the
dentry if there is a concurrent unlazy path walk. This is because
the dentry reference count will be at least 2 in this case causing
d_invalidate() to return EBUSY. So the asumption that the dentry
will be discarded then correctly instantiated via ->lookup() might
not hold.

Signed-off-by: Ian Kent <raven@themaw.net>
Reviewed-by: Jeff Layton <jlayton@redhat.com>
Cc: Steve French <smfrench@gmail.com>
Cc: linux-cifs@vger.kernel.org
Signed-off-by: Steve French <sfrench@us.ibm.com>

1 files changed, 12 insertions, 5 deletions

diff --git a/fs/cifs/dir.c b/fs/cifs/dir.c
index d172c8ed9017..ec4e9a2a12f8 100644
--- a/fs/cifs/dir.c
+++ b/fs/cifs/dir.c
@@ -668,12 +668,19 @@ cifs_d_revalidate(struct dentry *direntry, struct nameidata *nd)
                         return 0;
                 else {
                         /*
-                         * Forcibly invalidate automounting directory inodes
-                         * (remote DFS directories) so to have them
-                         * instantiated again for automount
+                         * If the inode wasn't known to be a dfs entry when
+                         * the dentry was instantiated, such as when created
+                         * via ->readdir(), it needs to be set now since the
+                         * attributes will have been updated by
+                         * cifs_revalidate_dentry().
                          */
-                        if (IS_AUTOMOUNT(direntry->d_inode))
-                                return 0;
+                        if (IS_AUTOMOUNT(direntry->d_inode) &&
+                           !(direntry->d_flags & DCACHE_NEED_AUTOMOUNT)) {
+                                spin_lock(&direntry->d_lock);
+                                direntry->d_flags |= DCACHE_NEED_AUTOMOUNT;
+                                spin_unlock(&direntry->d_lock);
+                        }
+
                         return 1;
                 }
         }