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SubjectRe: a problem tcp_v4_err()
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





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