Messages in this thread | | | Date | Tue, 16 Jun 2015 13:37:09 -0400 | From | Steven Rostedt <> | Subject | Re: call_rcu from trace_preempt |
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On Tue, 16 Jun 2015 10:20:05 -0700 Alexei Starovoitov <ast@plumgrid.com> wrote:
> 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.
Use a irq_work() handler to do the kfree_rcu(), and use llist (lockless list) to add items to the list.
-- Steve
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