autofs4 - dont clear DCACHE_NEED_AUTOMOUNT on rootless mount

The DCACHE_NEED_AUTOMOUNT flag is cleared on mount and set on expire
for autofs rootless multi-mount dentrys to prevent unnecessary calls
to ->d_automount().

Since DCACHE_MANAGE_TRANSIT is always set on autofs dentrys ->d_managed()
is always called so the check can be done in ->d_manage() without the
need to change the flag. This still avoids unnecessary calls to
->d_automount(), adds negligible overhead and eliminates a seriously
ugly check in the expire code.

Signed-off-by: Ian Kent <raven@themaw.net>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 36 insertions, 34 deletions

diff --git a/fs/autofs4/expire.c b/fs/autofs4/expire.c
index 842d00048a65..01443ce43ee7 100644
--- a/fs/autofs4/expire.c
+++ b/fs/autofs4/expire.c
@@ -548,15 +548,6 @@ int autofs4_do_expire_multi(struct super_block *sb, struct vfsmount *mnt,
 
                 spin_lock(&sbi->fs_lock);
                 ino->flags &= ~AUTOFS_INF_EXPIRING;
-                spin_lock(&dentry->d_lock);
-                if (!ret) {
-                        if ((IS_ROOT(dentry) ||
-                            (autofs_type_indirect(sbi->type) &&
-                             IS_ROOT(dentry->d_parent))) &&
-                            !(dentry->d_flags & DCACHE_NEED_AUTOMOUNT))
-                                __managed_dentry_set_automount(dentry);
-                }
-                spin_unlock(&dentry->d_lock);
                 complete_all(&ino->expire_complete);
                 spin_unlock(&sbi->fs_lock);
                 dput(dentry);
diff --git a/fs/autofs4/root.c b/fs/autofs4/root.c
index 91b11650722e..30a6ab66e99a 100644
--- a/fs/autofs4/root.c
+++ b/fs/autofs4/root.c
@@ -355,7 +355,6 @@ static struct vfsmount *autofs4_d_automount(struct path *path)
                 status = autofs4_mount_wait(dentry);
                 if (status)
                         return ERR_PTR(status);
-                spin_lock(&sbi->fs_lock);
                 goto done;
         }
 
@@ -364,8 +363,11 @@ static struct vfsmount *autofs4_d_automount(struct path *path)
          * having d_mountpoint() true, so there's no need to call back
          * to the daemon.
          */
-        if (dentry->d_inode && S_ISLNK(dentry->d_inode->i_mode))
+        if (dentry->d_inode && S_ISLNK(dentry->d_inode->i_mode)) {
+                spin_unlock(&sbi->fs_lock);
                 goto done;
+        }
+
         if (!d_mountpoint(dentry)) {
                 /*
                  * It's possible that user space hasn't removed directories
@@ -379,8 +381,10 @@ static struct vfsmount *autofs4_d_automount(struct path *path)
                  * require user space behave.
                  */
                 if (sbi->version > 4) {
-                        if (have_submounts(dentry))
+                        if (have_submounts(dentry)) {
+                                spin_unlock(&sbi->fs_lock);
                                 goto done;
+                        }
                 } else {
                         spin_lock(&dentry->d_lock);
                         if (!list_empty(&dentry->d_subdirs)) {
@@ -399,28 +403,8 @@ static struct vfsmount *autofs4_d_automount(struct path *path)
                         return ERR_PTR(status);
                 }
         }
-done:
-        if (!(ino->flags & AUTOFS_INF_EXPIRING)) {
-                /*
-                 * Any needed mounting has been completed and the path
-                 * updated so clear DCACHE_NEED_AUTOMOUNT so we don't
-                 * call ->d_automount() on rootless multi-mounts since
-                 * it can lead to an incorrect ELOOP error return.
-                 *
-                 * Only clear DMANAGED_AUTOMOUNT for rootless multi-mounts and
-                 * symlinks as in all other cases the dentry will be covered by
-                 * an actual mount so ->d_automount() won't be called during
-                 * the follow.
-                 */
-                spin_lock(&dentry->d_lock);
-                if ((!d_mountpoint(dentry) &&
-                    !list_empty(&dentry->d_subdirs)) ||
-                    (dentry->d_inode && S_ISLNK(dentry->d_inode->i_mode)))
-                        __managed_dentry_clear_automount(dentry);
-                spin_unlock(&dentry->d_lock);
-        }
         spin_unlock(&sbi->fs_lock);
-
+done:
         /* Mount succeeded, check if we ended up with a new dentry */
         dentry = autofs4_mountpoint_changed(path);
         if (!dentry)
@@ -432,6 +416,8 @@ done:
 int autofs4_d_manage(struct dentry *dentry, bool rcu_walk)
 {
         struct autofs_sb_info *sbi = autofs4_sbi(dentry->d_sb);
+        struct autofs_info *ino = autofs4_dentry_ino(dentry);
+        int status;
 
         DPRINTK("dentry=%p %.*s",
                 dentry, dentry->d_name.len, dentry->d_name.name);
@@ -456,7 +442,32 @@ int autofs4_d_manage(struct dentry *dentry, bool rcu_walk)
          * This dentry may be under construction so wait on mount
          * completion.
          */
-        return autofs4_mount_wait(dentry);
+        status = autofs4_mount_wait(dentry);
+        if (status)
+                return status;
+
+        spin_lock(&sbi->fs_lock);
+        /*
+         * If the dentry has been selected for expire while we slept
+         * on the lock then it might go away. We'll deal with that in
+         * ->d_automount() and wait on a new mount if the expire
+         * succeeds or return here if it doesn't (since there's no
+         * mount to follow with a rootless multi-mount).
+         */
+        if (!(ino->flags & AUTOFS_INF_EXPIRING)) {
+                /*
+                 * Any needed mounting has been completed and the path
+                 * updated so check if this is a rootless multi-mount so
+                 * we can avoid needless calls ->d_automount() and avoid
+                 * an incorrect ELOOP error return.
+                 */
+                if ((!d_mountpoint(dentry) && !simple_empty(dentry)) ||
+                    (dentry->d_inode && S_ISLNK(dentry->d_inode->i_mode)))
+                        status = -EISDIR;
+        }
+        spin_unlock(&sbi->fs_lock);
+
+        return status;
 }
 
 /* Lookups in the root directory */