uprobes: Change unregister/apply to WARN() if uprobe/consumer is gone

uprobes: Change unregister/apply to WARN() if uprobe/consumer is gone

Add WARN_ON's into uprobe_unregister() and uprobe_apply() to ensure
that nobody tries to play with the dead uprobe/consumer. This helps
to catch the bugs like the one fixed by the previous patch.

In the longer term we should fix this poorly designed interface.
uprobe_register() should return "struct uprobe *" which should be
passed to apply/unregister. Plus other semantic changes, see the
changelog in commit 41ccba029e94.

Link: http://lkml.kernel.org/p/[email protected]
Acked-by: Namhyung Kim <[email protected]>
Acked-by: Srikar Dronamraju <[email protected]>
Signed-off-by: Oleg Nesterov <[email protected]>
Signed-off-by: Steven Rostedt <[email protected]>