Re: a problem tcp_v4_err()

[Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>]

Hello!

On Fri, Nov 12, 2010 at 07:12:58PM +0100, Eric Dumazet wrote:
> I see socket is locked around line 368,
> 
>         bh_lock_sock(sk);
>         /* If too many ICMPs get dropped on busy
>          * servers this needs to be solved differently.
>          */
>         if (sock_owned_by_user(sk))
>                 NET_INC_STATS_BH(net, LINUX_MIB_LOCKDROPPEDICMPS);
> 
> 
> Hmm, maybe some goto is missing ;)

It is not missing, sock_owned_by_user() is checked later when some operation which
cannot be done without lock is required. It was done to save error in sk_err_soft even
when socket is locked.

This code also _understands_ this: look at

                } else if (sock_owned_by_user(sk)) {
                        /* RTO revert clocked out retransmission,
                         * but socket is locked. Will defer. */
                        inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
                                                  HZ/20, TCP_RTO_MAX);

but somehow it considers the manipulations with rto/backoff/write_queue as safe.
Seems, they are not.

Alexey