Merge branch 'for-3.10-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup

Pull cgroup fixes from Tejun Heo:

 - Fix for yet another xattr bug which may lead to NULL deref.

 - A subtle bug in for_each_descendant_pre().  This bug requires quite
   specific conditions to trigger and isn't too likely to actually
   happen in the wild, but maybe that just makes it that much more
   nastier.

 - A warning message added for silly cgroup re-mount (not -o remount,
   but unmount followed by mount) behavior.

* 'for-3.10-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup:
  cgroup: warn about mismatching options of a new mount of an existing hierarchy
  cgroup: fix a subtle bug in descendant pre-order walk
  cgroup: initialize xattr before calling d_instantiate()

1 files changed, 16 insertions, 15 deletions

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 2a9926275f80..a7c9e6ddb979 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -1686,11 +1686,14 @@ static struct dentry *cgroup_mount(struct file_system_type *fs_type,
                  */
                 cgroup_drop_root(opts.new_root);
 
-                if (((root->flags | opts.flags) & CGRP_ROOT_SANE_BEHAVIOR) &&
-                    root->flags != opts.flags) {
-                        pr_err("cgroup: sane_behavior: new mount options should match the existing superblock\n");
-                        ret = -EINVAL;
-                        goto drop_new_super;
+                if (root->flags != opts.flags) {
+                        if ((root->flags | opts.flags) & CGRP_ROOT_SANE_BEHAVIOR) {
+                                pr_err("cgroup: sane_behavior: new mount options should match the existing superblock\n");
+                                ret = -EINVAL;
+                                goto drop_new_super;
+                        } else {
+                                pr_warning("cgroup: new mount options do not match the existing superblock, will be ignored\n");
+                        }
                 }
 
                 /* no subsys rebinding, so refcounts don't change */
@@ -2699,13 +2702,14 @@ static int cgroup_add_file(struct cgroup *cgrp, struct cgroup_subsys *subsys,
                 goto out;
         }
 
+        cfe->type = (void *)cft;
+        cfe->dentry = dentry;
+        dentry->d_fsdata = cfe;
+        simple_xattrs_init(&cfe->xattrs);
+
         mode = cgroup_file_mode(cft);
         error = cgroup_create_file(dentry, mode | S_IFREG, cgrp->root->sb);
         if (!error) {
-                cfe->type = (void *)cft;
-                cfe->dentry = dentry;
-                dentry->d_fsdata = cfe;
-                simple_xattrs_init(&cfe->xattrs);
                 list_add_tail(&cfe->node, &parent->files);
                 cfe = NULL;
         }
@@ -2953,11 +2957,8 @@ struct cgroup *cgroup_next_descendant_pre(struct cgroup *pos,
         WARN_ON_ONCE(!rcu_read_lock_held());
 
         /* if first iteration, pretend we just visited @cgroup */
-        if (!pos) {
-                if (list_empty(&cgroup->children))
-                        return NULL;
+        if (!pos)
                 pos = cgroup;
-        }
 
         /* visit the first child if exists */
         next = list_first_or_null_rcu(&pos->children, struct cgroup, sibling);
@@ -2965,14 +2966,14 @@ struct cgroup *cgroup_next_descendant_pre(struct cgroup *pos,
                 return next;
 
         /* no child, visit my or the closest ancestor's next sibling */
-        do {
+        while (pos != cgroup) {
                 next = list_entry_rcu(pos->sibling.next, struct cgroup,
                                       sibling);
                 if (&next->sibling != &pos->parent->children)
                         return next;
 
                 pos = pos->parent;
-        } while (pos != cgroup);
+        }
 
         return NULL;
 }