tls: decrement decrypt_pending if no async completion will be called

With mixed sync/async decryption, or failures of crypto_aead_decrypt,
we increment decrypt_pending but we never do the corresponding
decrement since tls_decrypt_done will not be called. In this case, we
should decrement decrypt_pending immediately to avoid getting stuck.

For example, the prequeue prequeue test gets stuck with mixed
modes (one async decrypt + one sync decrypt).

Fixes: 94524d8f ("net/tls: Add support for async decryption of tls records")
Signed-off-by: Sabrina Dubroca <sd@queasysnail.net>
Link: https://lore.kernel.org/r/c56d5fc35543891d5319f834f25622360e1bfbec.1709132643.git.sd@queasysnail.netSigned-off-by: Jakub Kicinski <kuba@kernel.org>

net/tls/tls_sw.c

@@ -289,6 +289,8 @@ static int tls_do_decryption(struct sock *sk,
 			return 0;
 
 		ret = crypto_wait_req(ret, &ctx->async_wait);
+	} else if (darg->async) {
+		atomic_dec(&ctx->decrypt_pending);
 	}
 	darg->async = false;