Merge branch 'for-3.5-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj...

Merge branch 'for-3.5-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup

Pull cgroup fixes from Tejun Heo:
 "The previous cgroup pull request contained a patch to fix a race
  condition during cgroup hierarchy umount.  Unfortunately, while the
  patch reduced the race window such that the test case I and Sasha were
  using didn't trigger it anymore, it wasn't complete - Shyju and Li
  could reliably trigger the race condition using a different test case.

  The problem wasn't the gap between dentry deletion and release which
  the previous patch tried to fix.  The window was between the last
  dput() of a root's child and the resulting dput() of the root.  For
  cgroup dentries, the deletion and release always happen synchronously.
  As this releases the s_active ref, the refcnt of the root dentry,
  which doesn't hold s_active, stays above zero without the
  corresponding s_active.  If umount was in progress, the last
  deactivate_super() proceeds to destory the superblock and triggers
  BUG() on the non-zero root dentry refcnt after shrinking.

  This issue surfaced because cgroup dentries are now allowed to linger
  after rmdir(2) since 3.5-rc1.  Before, rmdir synchronously drained the
  dentry refcnt and the s_active acquired by rmdir from vfs layer
  protected the whole thing.  After 3.5-rc1, cgroup may internally hold
  and put dentry refs after rmdir finishes and the delayed dput()
  doesn't have surrounding s_active ref exposing this issue.

  This pull request contains two patches - one reverting the previous
  incorrect fix and the other adding the surrounding s_active ref around
  the delayed dput().

  This is quite late in the release cycle but the change is on the safer
  side and fixes the test cases reliably, so I don't think it's too
  crazy."

* 'for-3.5-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup:
  cgroup: fix cgroup hierarchy umount race
  Revert "cgroup: superblock can't be released with active dentries"