Messages in this thread | | | Date | Thu, 29 May 2014 18:50:57 +0200 | From | Peter Zijlstra <> | Subject | Re: perf: use after free in perf_remove_from_context |
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On Thu, May 29, 2014 at 12:44:23PM -0400, Sasha Levin wrote: > On 05/29/2014 11:07 AM, Peter Zijlstra wrote: > > On Thu, May 29, 2014 at 10:47:09AM -0400, Sasha Levin wrote: > >> It doesn't work out well because we later lock a mutex in sync_child_event(). > >> > > > > Urgh, right you are. I'll go stare at it more. It shouldn't have > > mattered, because the mutex we take just before should ensure existence, > > but.. you know.. :-) > > > > So the only caller to sync_child_event() is that loop. According to what you said > it should be safe to remove that mutex lock, but doing that triggers a list > corruption: > > [ 1204.341887] WARNING: CPU: 20 PID: 12839 at lib/list_debug.c:62 __list_del_entry+0xa1/0xe0() > [ 1204.347597] list_del corruption. next->prev should be ffff8806ca68b108, but was ffff88051a67c398 > [...] > > I don't see how that would happen :/
No, what I said is that the mutex in perf_event_exit_task() should be sufficient to guard the list iteration calling __perf_event_exit_task().
Ading the RCU was a bit of paranoia..
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