autofs4 - fix autofs4_expire_indirect() traversal

The vfs-scale changes changed the traversal used in
autofs4_expire_indirect() from a list to a depth first tree traversal
which isn't right.

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

1 files changed, 51 insertions, 1 deletions

diff --git a/fs/autofs4/expire.c b/fs/autofs4/expire.c
index c403abcc725b..bc482e07b925 100644
--- a/fs/autofs4/expire.c
+++ b/fs/autofs4/expire.c
@@ -87,6 +87,56 @@ done:
 }
 
 /*
+ * Calculate and dget next entry in the subdirs list under root.
+ */
+static struct dentry *get_next_positive_subdir(struct dentry *prev,
+                                                struct dentry *root)
+{
+        struct list_head *next;
+        struct dentry *p, *q;
+
+        spin_lock(&autofs4_lock);
+
+        if (prev == NULL) {
+                spin_lock(&root->d_lock);
+                prev = dget_dlock(root);
+                next = prev->d_subdirs.next;
+                p = prev;
+                goto start;
+        }
+
+        p = prev;
+        spin_lock(&p->d_lock);
+again:
+        next = p->d_u.d_child.next;
+start:
+        if (next == &root->d_subdirs) {
+                spin_unlock(&p->d_lock);
+                spin_unlock(&autofs4_lock);
+                dput(prev);
+                return NULL;
+        }
+
+        q = list_entry(next, struct dentry, d_u.d_child);
+
+        spin_lock_nested(&q->d_lock, DENTRY_D_LOCK_NESTED);
+        /* Negative dentry - try next */
+        if (!simple_positive(q)) {
+                spin_unlock(&p->d_lock);
+                p = q;
+                goto again;
+        }
+        dget_dlock(q);
+        spin_unlock(&q->d_lock);
+        spin_unlock(&p->d_lock);
+        spin_unlock(&autofs4_lock);
+
+        dput(prev);
+
+        return q;
+}
+
+/*
  * Calculate and dget next entry in top down tree traversal.
  */
 static struct dentry *get_next_positive_dentry(struct dentry *prev,
@@ -333,7 +383,7 @@ struct dentry *autofs4_expire_indirect(struct super_block *sb,
         timeout = sbi->exp_timeout;
 
         dentry = NULL;
-        while ((dentry = get_next_positive_dentry(dentry, root))) {
+        while ((dentry = get_next_positive_subdir(dentry, root))) {
                 spin_lock(&sbi->fs_lock);
                 ino = autofs4_dentry_ino(dentry);
                 /* No point expiring a pending mount */