ops_sem and tpm_mutex

[Jarkko Sakkinen <jarkko.sakkinen-VuQAYsv1563Yd54FQh9/CA@public.gmane.org>]

Hi

I started to looking at ops_sem and tpm_mutex because it would be nicer
to have one lock. When we do something that uses ops_sem we do this:

1. read lock for ops_sem
2. lock tpm_mutex

This is the basic pattern. Basically we always loose the benefit of
RW-lock because in every use case we also lock a mutex.

And the mutex of course cannot be taken off because we want to mutually
exclude the TPM access.

What I was thinking that maybe we could have kref for ops instead
of lock. In the places where we now use read lock you could use
kref_get_unless_zero() to avoid races with tpm_chip_unregister().

/Jarkko

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