Messages in this thread | | | Date | Tue, 16 Jun 2015 10:20:05 -0700 | From | Alexei Starovoitov <> | Subject | Re: call_rcu from trace_preempt |
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On 6/16/15 5:38 AM, Daniel Wagner wrote: > static int free_thread(void *arg) > +{ > + unsigned long flags; > + struct htab_elem *l; > + > + while (!kthread_should_stop()) { > + spin_lock_irqsave(&elem_freelist_lock, flags); > + while (!list_empty(&elem_freelist)) { > + l = list_entry(elem_freelist.next, > + struct htab_elem, list); > + list_del(&l->list); > + kfree(l);
that's not right, since such thread defeats rcu protection of lookup. We need either kfree_rcu/call_rcu or synchronize_rcu. Obviously the former is preferred that's why I'm still digging into it. Probably a thread that does kfree_rcu would be ok, but we shouldn't be doing it unconditionally. For all networking programs and 99% of tracing programs the existing code is fine and I don't want to slow it down to tackle the corner case. Extra spin_lock just to add it to the list is also quite costly.
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