On 06/03/2013 09:16 PM, Neil Horman wrote:

On Mon, Jun 03, 2013 at 05:55:06PM +0800, Ying Xue wrote:

quoted

On 05/31/2013 09:36 PM, Neil Horman wrote:

quoted

On Thu, May 30, 2013 at 03:36:06PM -0400, Paul Gortmaker wrote:

quoted

From: Jon Maloy <redacted>

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@tuxdriver.com>
Signed-off-by: Jon Maloy <redacted>
Signed-off-by: Paul Gortmaker <redacted>
---
 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