vfs - check non-mountpoint dentry might block in __follow_mount_rcu()

When following a mount in rcu-walk mode we must check if the incoming dentry
is telling us it may need to block, even if it isn't actually a mountpoint.

Signed-off-by: Ian Kent <raven@themaw.net>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 18 insertions, 5 deletions

diff --git a/fs/namei.c b/fs/namei.c
index d0066e17d45d..3cb616d38d9c 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -992,6 +992,12 @@ int follow_down_one(struct path *path)
         return 0;
 }
 
+static inline bool managed_dentry_might_block(struct dentry *dentry)
+{
+        return (dentry->d_flags & DCACHE_MANAGE_TRANSIT &&
+                dentry->d_op->d_manage(dentry, true) < 0);
+}
+
 /*
  * Skip to top of mountpoint pile in rcuwalk mode.  We abort the rcu-walk if we
  * meet a managed dentry and we're not walking to "..".  True is returned to
@@ -1000,19 +1006,26 @@ int follow_down_one(struct path *path)
 static bool __follow_mount_rcu(struct nameidata *nd, struct path *path,
                                struct inode **inode, bool reverse_transit)
 {
-        while (d_mountpoint(path->dentry)) {
+        for (;;) {
                 struct vfsmount *mounted;
-                if (unlikely(path->dentry->d_flags & DCACHE_MANAGE_TRANSIT) &&
-                    !reverse_transit &&
-                    path->dentry->d_op->d_manage(path->dentry, true) < 0)
+                /*
+                 * Don't forget we might have a non-mountpoint managed dentry
+                 * that wants to block transit.
+                 */
+                *inode = path->dentry->d_inode;
+                if (!reverse_transit &&
+                     unlikely(managed_dentry_might_block(path->dentry)))
                         return false;
+
+                if (!d_mountpoint(path->dentry))
+                        break;
+
                 mounted = __lookup_mnt(path->mnt, path->dentry, 1);
                 if (!mounted)
                         break;
                 path->mnt = mounted;
                 path->dentry = mounted->mnt_root;
                 nd->seq = read_seqcount_begin(&path->dentry->d_seq);
-                *inode = path->dentry->d_inode;
         }
 
         if (unlikely(path->dentry->d_flags & DCACHE_NEED_AUTOMOUNT))