KEYS: Add missing smp_rmb() primitives to the keyring search code

KEYS: Add missing smp_rmb() primitives to the keyring search code

Add missing smp_rmb() primitives to the keyring search code.

When keyring payloads are appended to without replacement (thus using up spare
slots in the key pointer array), an smp_wmb() is issued between the pointer
assignment and the increment of the key count (nkeys).

There should be corresponding read barriers between the read of nkeys and
dereferences of keys[n] when n is dependent on the value of nkeys.

Signed-off-by: David Howells <[email protected]>
Reviewed-by: Paul E. McKenney <[email protected]>
Signed-off-by: James Morris <[email protected]>