Em 19-01-2016 17:55, Vlad Yasevich escreveu:
On 01/19/2016 02:31 PM, Marcelo Ricardo Leitner wrote:
Em 19-01-2016 16:37, Vlad Yasevich escreveu:
On 01/19/2016 10:59 AM, Marcelo Ricardo Leitner wrote:
Yes, not thrilled here either about connect-to-self.
But there is a big difference on how both works. For rx we can just look for wanted skbs
in rx queue, as they aren't going anywhere, but for tx I don't think we can easily block
sctp_wfree() call because that may be happening on another CPU (or am I mistaken here?
sctp still doesn't have RFS but even irqbalance could affect this AFAICT) and more than
one skb may be in transit at a time.
The way it's done now, we wouldn't have to block sctp_wfree. Chunks are released under
lock when they are acked, so we are OK here. The tx completions will just put 1 byte back
to the socket associated with the tx'ed skb, and that should still be ok as
sctp_packet_release_owner will call sk_free().
Please let me rephrase it. I'm actually worried about the asoc->base.sk part of the story
and how it's fetched in sctp_wfree(). I think we can update that sk pointer after
sock_wfree() has fetched it but not used it yet, possibly leading to accounting it twice,
one during migration and one on sock_wfree.
In sock_wfree() it will update some sk stats like sk->sk_wmem_alloc, among others.
sctp_wfree() is only used on skbs that were created as sctp chunks to be transmitted.
Right now, these skbs aren't actually submitted to the IP or to nic to be transmitted.
They are queued at the association level (either in transports or in the outqueue).
They are only freed during ACK processing.
The ACK processing happens under a socket lock and thus asoc->base.sk can not move.
The migration process also happens under a socket lock. As a result, during migration
we are guaranteed the chunk queues remain consistent and that asoc->base.sk linkage
remains consistent. In fact, if you look at the sctp_sock_migrate, we lock both
sockets when we reassign the assoc->base.sk so we know both sockets are properly locked.
So, I am not sure that what you are worried about can happen. Please feel free to
double-check the above of course.
Ohh, right. That makes sense. I'll rework the patch. Thanks Vlad.
Marcelo
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