lockdep: Check the depth of subclass

Current look_up_lock_class() doesn't check the parameter "subclass".
This rarely rises problems because the main caller of this function,
register_lock_class(), checks it.

But register_lock_class() is not the only function which calls
look_up_lock_class(). lock_set_class() and its callees also call it.
And lock_set_class() doesn't check this parameter.

This will rise problems when the the value of subclass is larger than
MAX_LOCKDEP_SUBCLASSES. Because the address (used as the key of class)
caliculated with too large subclass has a probability to point
another key in different lock_class_key.

Of course this problem depends on the memory layout and
occurs with really low probability.

Signed-off-by: Hitoshi Mitake <[email protected]>
Cc: Dmitry Torokhov <[email protected]>
Cc: Vojtech Pavlik <[email protected]>
Cc: Frederic Weisbecker <[email protected]>
Signed-off-by: Peter Zijlstra <[email protected]>
LKML-Reference: <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>

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