netdev - Re: [PATCH] UDPCP Communication Protocol

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Message-ID: <1293794758.2973.49.camel@edumazet-laptop>
Date:	Fri, 31 Dec 2010 12:25:58 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	stefani@...bold.net
Cc:	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	davem@...emloft.net, netdev@...r.kernel.org
Subject: Re: [PATCH] UDPCP Communication Protocol

Le vendredi 31 décembre 2010 à 10:29 +0100, stefani@...bold.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().



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