keys: Provide a key_try_get() function and use it

Add a key_try_get() function to try to get a ref on a key and switch code
that's manipulating the key refcount directly to use it.  This will allow a
tracepoint to be emplaced there later.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Jarkko Sakkinen <jarkko@kernel.org>
cc: keyrings@vger.kernel.org
cc: linux-security-module@vger.kernel.org
3 files changed