Allow d_manage() to be used in RCU-walk mode

Allow d_manage() to be called from pathwalk when it is in RCU-walk mode as well
as when it is in Ref-walk mode.  This permits __follow_mount_rcu() to call
d_manage() directly.  d_manage() needs a parameter to indicate that it is in
RCU-walk mode as it isn't allowed to sleep if in that mode (but should return
-ECHILD instead).

autofs4_d_manage() can then be set to retain RCU-walk mode if the daemon
accesses it and otherwise request dropping back to ref-walk mode.

Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 8 insertions, 7 deletions

diff --git a/fs/namei.c b/fs/namei.c
index 373852012713..5c89695ae1e4 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -987,7 +987,8 @@ static int follow_managed(struct path *path, unsigned flags)
                 if (managed & DCACHE_MANAGE_TRANSIT) {
                         BUG_ON(!path->dentry->d_op);
                         BUG_ON(!path->dentry->d_op->d_manage);
-                        ret = path->dentry->d_op->d_manage(path->dentry, false);
+                        ret = path->dentry->d_op->d_manage(path->dentry,
+                                                           false, false);
                         if (ret < 0)
                                 return ret == -EISDIR ? 0 : ret;
                 }
@@ -1048,13 +1049,12 @@ int follow_down_one(struct path *path)
 static bool __follow_mount_rcu(struct nameidata *nd, struct path *path,
                                struct inode **inode, bool reverse_transit)
 {
-        unsigned abort_mask =
-                reverse_transit ? 0 : DCACHE_MANAGE_TRANSIT;
-
         while (d_mountpoint(path->dentry)) {
                 struct vfsmount *mounted;
-                if (path->dentry->d_flags & abort_mask)
-                        return true;
+                if (unlikely(path->dentry->d_flags & DCACHE_MANAGE_TRANSIT) &&
+                    !reverse_transit &&
+                    path->dentry->d_op->d_manage(path->dentry, false, true) < 0)
+                        return false;
                 mounted = __lookup_mnt(path->mnt, path->dentry, 1);
                 if (!mounted)
                         break;
@@ -1132,7 +1132,8 @@ int follow_down(struct path *path, bool mounting_here)
                 if (managed & DCACHE_MANAGE_TRANSIT) {
                         BUG_ON(!path->dentry->d_op);
                         BUG_ON(!path->dentry->d_op->d_manage);
-                        ret = path->dentry->d_op->d_manage(path->dentry, mounting_here);
+                        ret = path->dentry->d_op->d_manage(
+                                path->dentry, mounting_here, false);
                         if (ret < 0)
                                 return ret == -EISDIR ? 0 : ret;
                 }