[PATCH] perf/core: clear sibling list of detached events (was "Re: [PATCH] perf: Fix sibling iteration")

[Mark Rutland]

On Fri, Mar 16, 2018 at 11:50:17AM +0100, Peter Zijlstra wrote:
> On Fri, Mar 16, 2018 at 11:39:46AM +0100, Jiri Olsa wrote:
> > On Fri, Mar 16, 2018 at 11:31:29AM +0100, Peter Zijlstra wrote:

> > > There is at least one more known issue with that patch, but neither Mark
> > > nor me could reproduce so far, so we don't know if we're right about the
> > > cause.
> > 
> > is there more info about that issue? I could try it
> 
> Find below, 0day report didn't go out to lkml. We think moving the
> list_del_init() out from the !RB_NODE_EMPTY() test might fix, but since
> we can't repro so far, its all guesses.

In testing, I can see this always fires after we perf_group_detach() a
leader whose group_node is empty.

With the list_del_init() pulled out of that check, I see that we still
hit the leaders with an empty group_node (with a hacked-in WARN_ON), but
no longer blow up in a subsequent perf_group_detach().

I've given this 50 boots with the 0day scripts, and no explosions so far
(with 5 boots where a leader had an empty group_node).

Thanks,
Mark.

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