linux-kernel - Re: [PATCH net] rxrpc: Call state should be read with READ

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Date:   Tue, 12 Jan 2021 18:25:33 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     David Howells <dhowells@...hat.com>
Cc:     netdev@...r.kernel.org,
        Baptiste Lepers <baptiste.lepers@...il.com>,
        linux-afs@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net] rxrpc: Call state should be read with READ_ONCE()
 under some circumstances

On Tue, 12 Jan 2021 15:59:15 +0000 David Howells wrote:
> From: Baptiste Lepers <baptiste.lepers@...il.com>
> 
> The call state may be changed at any time by the data-ready routine in
> response to received packets, so if the call state is to be read and acted
> upon several times in a function, READ_ONCE() must be used unless the call
> state lock is held.
> 
> As it happens, we used READ_ONCE() to read the state a few lines above the
> unmarked read in rxrpc_input_data(), so use that value rather than
> re-reading it.
> 
> Signed-off-by: Baptiste Lepers <baptiste.lepers@...il.com>
> Signed-off-by: David Howells <dhowells@...hat.com>

Fixes: a158bdd3247b ("rxrpc: Fix call timeouts")

maybe?

> diff --git a/net/rxrpc/input.c b/net/rxrpc/input.c
> index 667c44aa5a63..dc201363f2c4 100644
> --- a/net/rxrpc/input.c
> +++ b/net/rxrpc/input.c
> @@ -430,7 +430,7 @@ static void rxrpc_input_data(struct rxrpc_call *call, struct sk_buff *skb)
>  		return;
>  	}
>  
> -	if (call->state == RXRPC_CALL_SERVER_RECV_REQUEST) {
> +	if (state == RXRPC_CALL_SERVER_RECV_REQUEST) {
>  		unsigned long timo = READ_ONCE(call->next_req_timo);
>  		unsigned long now, expect_req_by;
>  
> 
>