Eric Dumazet <eric.duma...@gmail.com> writes:
> On Mon, 2015-10-05 at 17:31 +0100, Rainer Weikusat wrote:
>
>> atomic_long_set(&u->inflight, 0);
>> INIT_LIST_HEAD(&u->link);
>> @@ -2135,8 +2139,16 @@ static unsigned int unix_poll(struct fil
>> static unsigned int unix_dgram_poll(struct file *file, struct socket *sock,
>> poll_table *wait)
>> {
>> - struct sock *sk = sock->sk, *other;
>> - unsigned int mask, writable;
>> + struct sock *sk = sock->sk, *other, *pp;
>> + struct unix_sock *u;
>> + unsigned int mask, writable, dead;
>> +
>> + u = unix_sk(sk);
>> + pp = u->poll_peer;
>> + if (pp) {
>> + u->poll_peer = NULL;
>> + sock_put(pp);
>> + }
>
>
> This looks racy.
> Multiple threads could use poll() at the same time,
> and you would have too many sock_put()
That's one of the reasons why I wrote "might work": The use of a single
structure member without any locking for the sock_poll_wait suggests
that this is taken care of in some other way, as does the absence of any
comment about that in the 'public' LDDs ("Linux Device Drivers"),
however, I don't really know if this is true. If not, this simple idea
can't work.
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