freezer: add unsafe versions of freezable helpers for NFS
NFS calls the freezable helpers with locks held, which is unsafe and will cause lockdep warnings when 6aa97070 "lockdep: check that no locks held at freeze time" is reapplied (it was reverted in dbf520a9). NFS shouldn't be doing this, but it has long-running syscalls that must hold a lock but also shouldn't block suspend. Until NFS freeze handling is rewritten to use a signal to exit out of the critical section, add new *_unsafe versions of the helpers that will not run the lockdep test when 6aa97070 is reapplied, and call them from NFS. In practice the likley result of holding the lock while freezing is that a second task blocked on the lock will never freeze, aborting suspend, but it is possible to manufacture a case using the cgroup freezer, the lock, and the suspend freezer to create a deadlock. Silencing the lockdep warning here will allow problems to be found in other drivers that may have a more serious deadlock risk, and prevent new problems from being added. Signed-off-by: NColin Cross <ccross@android.com> Acked-by: NPavel Machek <pavel@ucw.cz> Acked-by: NTejun Heo <tj@kernel.org> Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>
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