Re: [PATCH 2/9] PKT_SCHED: tc filter extension API

[Thomas Graf <tgraf@xxxxxxx>]

* Patrick McHardy <41D55FC9.6040605@xxxxxxxxx> 2004-12-31 15:18
> Thomas Graf wrote:
> >             struct tc_action *act;
> >             act = xchg(&dst->action, src->action);
> >             if (act)
> >                     tcf_action_destroy(act, TCA_ACT_UNBIND);
> >
> >Am I missing something?
> 
> Yes, the xchg without locking is only right in case we don't have
> an existing action that needs to be destroyed. Someone might still
> be looking at the old action in a softirq. If you want to keep the
> "lockless" variant, you need to call synchronize_net() before
> tcf_action_destroy().

You're absolutely right. I will put locks around it again to avoid
having the pointer exchanged in the middle of a classification.
A synchronize_net will avoid the crash but will no prevent a
possible corruption of the classification result if the action is used
more than once.