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Date: Tue, 4 Jun 2013 09:40:59 -0400
From: Neil Horman <nhorman@...driver.com>
To: Ying Xue <ying.xue@...driver.com>
Cc: Paul Gortmaker <paul.gortmaker@...driver.com>,
David Miller <davem@...emloft.net>, netdev@...r.kernel.org,
Jon Maloy <jon.maloy@...csson.com>,
Erik Hugne <erik.hugne@...csson.com>
Subject: Re: [PATCH net-next 01/12] tipc: change socket buffer overflow
control to respect sk_rcvbuf
On Tue, Jun 04, 2013 at 09:37:54AM +0800, Ying Xue wrote:
> On 06/03/2013 09:16 PM, Neil Horman wrote:
> > On Mon, Jun 03, 2013 at 05:55:06PM +0800, Ying Xue wrote:
> >> On 05/31/2013 09:36 PM, Neil Horman wrote:
> >>> On Thu, May 30, 2013 at 03:36:06PM -0400, Paul Gortmaker wrote:
> >>>> From: Jon Maloy <jon.maloy@...csson.com>
> >>>>
> >>>> As per feedback from the netdev community, we change the buffer
> >>>> overflow protection algorithm in receiving sockets so that it
> >>>> always respects the nominal upper limit set in sk_rcvbuf.
> >>>>
> >>>> Instead of scaling up from a small sk_rcvbuf value, which leads to
> >>>> violation of the configured sk_rcvbuf limit, we now calculate the
> >>>> weighted per-message limit by scaling down from a much bigger value,
> >>>> still in the same field, according to the importance priority of the
> >>>> received message.
> >>>>
> >>>> Cc: Neil Horman <nhorman@...driver.com>
> >>>> Signed-off-by: Jon Maloy <jon.maloy@...csson.com>
> >>>> Signed-off-by: Paul Gortmaker <paul.gortmaker@...driver.com>
> >>>> ---
> >>>> net/tipc/socket.c | 13 +++++++------
> >>>> 1 file changed, 7 insertions(+), 6 deletions(-)
> >>>>
> >>>> diff --git a/net/tipc/socket.c b/net/tipc/socket.c
> >>>> index 515ce38..2dfabc7 100644
> >>>> --- a/net/tipc/socket.c
> >>>> +++ b/net/tipc/socket.c
> >>>> @@ -1,7 +1,7 @@
> >>>> /*
> >>>> * net/tipc/socket.c: TIPC socket API
> >>>> *
> >>>> - * Copyright (c) 2001-2007, 2012 Ericsson AB
> >>>> + * Copyright (c) 2001-2007, 2012-2013, Ericsson AB
> >>>> * Copyright (c) 2004-2008, 2010-2012, Wind River Systems
> >>>> * All rights reserved.
> >>>> *
> >>>> @@ -203,6 +203,7 @@ static int tipc_create(struct net *net, struct socket *sock, int protocol,
> >>>>
> >>>> sock_init_data(sock, sk);
> >>>> sk->sk_backlog_rcv = backlog_rcv;
> >>>> + sk->sk_rcvbuf = CONN_OVERLOAD_LIMIT;
> >>> The last time Jon and I discussed this, I thought the consensus was to export
> >>> sk_rcvbuf via its own sysctl, or tie it to sysctl_rmem (while requiring a
> >>> protocol specific minimum on top of that), so administrators on memory
> >>> constrained systems didn't wonder why their sysctl changes weren't being
> >>> honored.
> >>
> >> Yes, your suggestion is reasonable, and I prefer to involve
> >> net.tipc.sysctl_rmem. But I have one question about it:
> >>
> >> As you suggested as belows, the default value of sk->sk_rcvbuf is set to
> >> sk->sk_rcvbuf >> 4 << msg_importance(TIPC_CRITICAL_IMPORTANCE), that is,
> >> sk->sk_rcvbuf is about 32MB.
> >>
> >> However, please see below code:
> >>
> >> int sock_setsockopt()
> >> {
> >> ...
> >> case SO_RCVBUF:
> >> /* Don't error on this BSD doesn't and if you think
> >> * about it this is right. Otherwise apps have to
> >> * play 'guess the biggest size' games. RCVBUF/SNDBUF
> >> * are treated in BSD as hints
> >> */
> >> val = min_t(u32, val, sysctl_rmem_max);
> >> set_rcvbuf:
> >> sk->sk_userlocks |= SOCK_RCVBUF_LOCK;
> >> /*
> >> * We double it on the way in to account for
> >> * "struct sk_buff" etc. overhead. Applications
> >> * assume that the SO_RCVBUF setting they make will
> >> * allow that much actual data to be received on that
> >> * socket.
> >> *
> >> * Applications are unaware that "struct sk_buff" and
> >> * other overheads allocate from the receive buffer
> >> * during socket buffer allocation.
> >> *
> >> * And after considering the possible alternatives,
> >> * returning the value we actually used in getsockopt
> >> * is the most desirable behavior.
> >> */
> >> sk->sk_rcvbuf = max_t(u32, val * 2, SOCK_MIN_RCVBUF);
> >> break;
> >> ...
> >> }
> >>
> >> From above logic of setting sk->sk_rcvbuf with SO_RCVBUF, it only
> >> permits the maximum value of sk->sk_rcvbuf to sysctl_rmem_max * 2(ie,
> >> about 400KB normally).
> >>
> >> So, even if the default value of sk->sk_rcvbuf is set to 32MB with
> >> net.tipc.sysctl_rmem, a bit smaller value than the default value can
> >> never be set to sk->sk_rcvbuf successfully with SO_RCVBUF option.
> >>
> >> How can we avoid the limit?
> >>
> > By administratively adjusting sysctl_rmem_max to be a sufficiently large value
> > such that using SO_RCVBUF won't be clamed to a lower limit.
> >
> > If you don't want to force users to have to manually adjust the sysctl, there
> > might be support for you to automatically update sysctl_rmem_max in your
> > tipc_init routine, and print an informational message indicating that tipc
> > requires the additional space (although I still maintain its not strictly
> > needed, but thats another argument).
> >
>
> Thanks for your clear clarification.
>
> I also have the same concern. If we override sysctl_rmem_max in
> tipc_init() with a larger value, I am afraid that other guys will oppose
> the behaviour.
>
> The truth is that little TIPC user adjusts the sk->sk_rcvbuf with
> SO_RCVBUF option in practice. If he really wants to do, he should follow
> your suggestion he manually enlarges the sysctl.
>
> OK, I will rewrite the patch with your suggestion.
>
> Regards,
> Ying
>
> > Neil
> >
> >
> >
>
>
Sounds good, thanks!
Neil
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