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Subject: Re: [PATCH] UDPCP Communication Protocol
From: Eric Dumazet <eric.dumazet@gmail.com>
To: stefani@seibold.net
Cc: linux-kernel@vger.kernel.org, akpm@linux-foundation.org,
        davem@davemloft.net, netdev@vger.kernel.org
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References: <1293787785-3834-1-git-send-email-stefani@seibold.net>
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Date: Fri, 31 Dec 2010 12:25:58 +0100
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Le vendredi 31 décembre 2010 à 10:29 +0100, stefani@seibold.net a
écrit :
> +		if (!list_empty(&usk->destlist)) {
> +			state->sk = (struct sock *)usk;
> +			state->dest = list_first_entry(&usk->destlist,
> +					struct udpcp_dest, list);
> +			sock_hold(state->sk);
> +
> +			if (atomic_read(&state->sk->sk_refcnt) != 1) {
> +				spin_unlock_irqrestore(&spinlock, flags);
> +				return state;
> +			}
> +			atomic_dec(&state->sk->sk_refcnt);
> +		}
> +

I am trying to understand what you are doing here.

It seems racy to me.

Apparently, what you want is to take a reference only if actual
sk_refcnt is not zero.

I suggest using atomic_inc_notzero(&state->sk->sk_refcnt) to avoid the
race in atomic_dec().