Re: [PATCH net-next v2 2/2] tcp_diag: report TCP MD5 signing keys and addresses

On Sat, 2017-08-26 at 07:53 +0200, Ivan Delalande wrote:

Sorry, I probably should have detailed my changes. I tried to address
this by locking the whole socket in the caller, tcp_diag_get_aux, just
outside of the rcu_read_lock. Would this work here, or do you see a
better way?

locking the socket is problematic.

It is already done in tcp_get_info() since linux-4.10 and unfortunately
it added unreasonable stall when a socket is flooded with tiny SACK
messages (socket backlog is huge)

People are now making tcp_rmem and tcp_wmem much bigger to allow BBR
flows to reach line rate on very long distance communications.

We are working to make tcp_rack_mark_lost() not having O(N) behavior,
but it is not done yet.


I would stick to RCU, but add sanity checks, so that _if_ the list is
different on the second RCU list traversal, you make sure :

1) We do not try to put more data in the reserved space

2) We memset(ptr, 0, remaining) the remaining space if we found less
entries in the 2nd loop.