netdev - Re: [PATCH net 1/2] net/tls: Replace TLS_RX_SYNC

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Date:   Mon, 24 May 2021 09:05:29 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Maxim Mikityanskiy <maximmi@...dia.com>
Cc:     Boris Pismenny <borisp@...dia.com>,
        John Fastabend <john.fastabend@...il.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        "David S. Miller" <davem@...emloft.net>,
        "Aviad Yehezkel" <aviadye@...dia.com>,
        Tariq Toukan <tariqt@...dia.com>, <netdev@...r.kernel.org>
Subject: Re: [PATCH net 1/2] net/tls: Replace TLS_RX_SYNC_RUNNING with RCU

On Mon, 24 May 2021 15:12:19 +0300 Maxim Mikityanskiy wrote:
> RCU synchronization is guaranteed to finish in finite time, unlike a
> busy loop that polls a flag. This patch is a preparation for the bugfix
> in the next patch, where the same synchronize_net() call will also be
> used to sync with the TX datapath.
> 
> Signed-off-by: Maxim Mikityanskiy <maximmi@...dia.com>
> Reviewed-by: Tariq Toukan <tariqt@...dia.com>
> ---
>  include/net/tls.h    |  1 -
>  net/tls/tls_device.c | 10 +++-------
>  2 files changed, 3 insertions(+), 8 deletions(-)
> 
> diff --git a/include/net/tls.h b/include/net/tls.h
> index 3eccb525e8f7..6531ace2a68b 100644
> --- a/include/net/tls.h
> +++ b/include/net/tls.h
> @@ -193,7 +193,6 @@ struct tls_offload_context_tx {
>  	(sizeof(struct tls_offload_context_tx) + TLS_DRIVER_STATE_SIZE_TX)
>  
>  enum tls_context_flags {
> -	TLS_RX_SYNC_RUNNING = 0,
>  	/* Unlike RX where resync is driven entirely by the core in TX only
>  	 * the driver knows when things went out of sync, so we need the flag
>  	 * to be atomic.
> diff --git a/net/tls/tls_device.c b/net/tls/tls_device.c
> index 76a6f8c2eec4..171752cd6910 100644
> --- a/net/tls/tls_device.c
> +++ b/net/tls/tls_device.c
> @@ -680,15 +680,13 @@ static void tls_device_resync_rx(struct tls_context *tls_ctx,
>  	struct tls_offload_context_rx *rx_ctx = tls_offload_ctx_rx(tls_ctx);
>  	struct net_device *netdev;
>  
> -	if (WARN_ON(test_and_set_bit(TLS_RX_SYNC_RUNNING, &tls_ctx->flags)))
> -		return;
> -
>  	trace_tls_device_rx_resync_send(sk, seq, rcd_sn, rx_ctx->resync_type);
> +	rcu_read_lock();
>  	netdev = READ_ONCE(tls_ctx->netdev);
>  	if (netdev)
>  		netdev->tlsdev_ops->tls_dev_resync(netdev, sk, seq, rcd_sn,
>  						   TLS_OFFLOAD_CTX_DIR_RX);

Now this can't sleep right? No bueno.

> -	clear_bit_unlock(TLS_RX_SYNC_RUNNING, &tls_ctx->flags);
> +	rcu_read_unlock();
>  	TLS_INC_STATS(sock_net(sk), LINUX_MIB_TLSRXDEVICERESYNC);
>  }
>