where crypto_invoke() returns ERESTART and before we set cc_qblocked to 1,
crypto_unblock() is called and sets it to 0. This way we mark device as
blocked forever.
Fix it by not setting cc_qblocked in the fast path and by protecting
crypto_invoke() in the crypto_proc thread with CRYPTO_Q_LOCK().
This won't slow things down, because there is no contention - we have
only one crypto thread. Actually it can be slightly faster, because we
save two atomic ops per crypto request.
The fast code path remains lock-less.
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