On Wed, Nov 11, 2015, at 20:28, Eric Dumazet wrote:
> On Wed, 2015-11-11 at 20:14 +0100, Hannes Frederic Sowa wrote:
> > On Wed, Nov 11, 2015, at 19:58, Eric Dumazet wrote:
>
> > Can you elaborate?
> >
> > I use tail as a cookie and check if we already tried to append to the
> > same tail skb with skb_append_pagefrags. If during allocation, which we
> > do outside of the locks, a new skb arrives, we take that and try to
> > append again (and free the old skb), to correctly not create any
> > reordering in the data stream.
> >
> > You think that tail could be reused in the meanwhile?
>
> Hmmm, there is some funky stuff at least.
>
> Are you sure the __skb_queue_tail(&other->sk_receive_queue, newskb)
> is appropriate ?
>
> (Why not locking sk_receive_queue is safe ?)
We hold the other's state lock at that time.
But I see another problem in unix_stream_read_generic:
/* Mark read part of skb as used */
if (!(flags & MSG_PEEK)) {
UNIXCB(skb).consumed += chunk;
sk_peek_offset_bwd(sk, chunk);
if (UNIXCB(skb).fp)
unix_detach_fds(&scm, skb);
if (unix_skb_len(skb))
break;
skb_unlink(skb, &sk->sk_receive_queue);
consume_skb(skb);
if (scm.fp)
break;
The skb_unlink happens solely on the list lock and not on the state lock
of the sk, so it is not synchronized to the other locks.
Bye,
Hannes
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