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Groups > linux.kernel > #1166278
| From | Alexei Starovoitov <ast@plumgrid.com> |
|---|---|
| Newsgroups | linux.kernel |
| Subject | Re: call_rcu from trace_preempt |
| Date | 2015-06-16 19:30 +0200 |
| Message-ID | <pC2Qr-GT-29@gated-at.bofh.it> (permalink) |
| References | (2 earlier) <pBNHI-3WS-3@gated-at.bofh.it> <pBODL-5mO-1@gated-at.bofh.it> <pBRUZ-1yj-9@gated-at.bofh.it> <pBYa7-2jk-13@gated-at.bofh.it> <pBYjN-2uo-17@gated-at.bofh.it> |
| Organization | linux.* mail to news gateway |
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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Re: call_rcu from trace_preempt Alexei Starovoitov <ast@plumgrid.com> - 2015-06-16 03:20 +0200
Re: call_rcu from trace_preempt Alexei Starovoitov <ast@plumgrid.com> - 2015-06-16 19:30 +0200
Re: call_rcu from trace_preempt Steven Rostedt <rostedt@goodmis.org> - 2015-06-16 19:40 +0200
Re: call_rcu from trace_preempt "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-06-17 22:40 +0200
Re: call_rcu from trace_preempt Alexei Starovoitov <ast@plumgrid.com> - 2015-06-17 23:00 +0200
Re: call_rcu from trace_preempt "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-06-17 23:40 +0200
Re: call_rcu from trace_preempt Alexei Starovoitov <ast@plumgrid.com> - 2015-06-18 02:00 +0200
Re: call_rcu from trace_preempt "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-06-18 02:30 +0200
Re: call_rcu from trace_preempt "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-06-16 19:50 +0200
Re: call_rcu from trace_preempt Steven Rostedt <rostedt@goodmis.org> - 2015-06-16 21:00 +0200
Re: call_rcu from trace_preempt "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-06-16 21:30 +0200
Re: call_rcu from trace_preempt Steven Rostedt <rostedt@goodmis.org> - 2015-06-16 21:30 +0200
Re: call_rcu from trace_preempt "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-06-16 21:40 +0200
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