On Wed, Nov 07, 2012 at 12:52:14PM +0000, David Woodhouse wrote:
>
> diff --git a/net/atm/pppoatm.c b/net/atm/pppoatm.c
> index 7507c20..56ad541 100644
> --- a/net/atm/pppoatm.c
> +++ b/net/atm/pppoatm.c
> @@ -283,11 +283,11 @@ static int pppoatm_send(struct ppp_channel *chan,
> struct sk_buff *skb)
> vcc = ATM_SKB(skb)->vcc;
> bh_lock_sock(sk_atm(vcc));
> if (sock_owned_by_user(sk_atm(vcc)))
> - goto nospace;
> + goto nospace_sched_wakeup;
> if (test_bit(ATM_VF_RELEASED, &vcc->flags)
> - || test_bit(ATM_VF_CLOSE, &vcc->flags)
> - || !test_bit(ATM_VF_READY, &vcc->flags))
> - goto nospace;
> + || test_bit(ATM_VF_CLOSE, &vcc->flags)
> + || !test_bit(ATM_VF_READY, &vcc->flags))
> + goto nospace_sched_wakeup;
>
> switch (pvcc->encaps) { /* LLC encapsulation needed */
> case e_llc:
> @@ -328,7 +328,17 @@ static int pppoatm_send(struct ppp_channel *chan, struct
> sk_buff *skb)
> ? DROP_PACKET : 1;
> bh_unlock_sock(sk_atm(vcc));
> return ret;
> -nospace:
> + nospace_sched_wakeup:
> + /* If we're returning zero for reasons *other* than the queue
> + * being full, then we need to ensure that a wakeup will
> + * happen and not just leave the channel stalled for ever.
> + * Just schedule the wakeup tasklet directly. As observed in
> + * pppoatm_pop(), it'll take the channel's ->downl lock which
> + * is also held by our caller, so it can't happen "too soon"
> + * and cause us to effectively miss a wakeup.
> + */
> + tasklet_schedule(&pvcc->wakeup_tasklet);
With this tasklet_schedule() we implement a "spin_lock" here, but in
this case both conditions (vcc not ready and socket locked) can be true
for a long time and we can spin here for a long time. I confirmed it by
reverting patch 1 (atm: detach protocol before closing vcc) and now
I have 50% of CPU used by ksoftirqd and 50% by pppd (UP system).
Krzysiek
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