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Date: Thu, 29 May 2014 12:52:53 -0400
From: Sasha Levin <sasha.levin@oracle.com>
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To: Peter Zijlstra <peterz@infradead.org>
CC: Ingo Molnar <mingo@kernel.org>, acme@ghostprotocols.net,
        LKML <linux-kernel@vger.kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>, Dave Jones <davej@redhat.com>
Subject: Re: perf: use after free in perf_remove_from_context
References: <5370EBE9.6@oracle.com> <20140514162943.GR30445@twins.programming.kicks-ass.net> <53739A9A.5010703@oracle.com> <20140514163535.GS30445@twins.programming.kicks-ass.net> <538676A7.6090306@oracle.com> <20140529075723.GA30445@twins.programming.kicks-ass.net> <5387486D.20108@oracle.com> <20140529150705.GJ19143@laptop.programming.kicks-ass.net> <538763E7.6030902@oracle.com> <20140529165057.GK19143@laptop.programming.kicks-ass.net>
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On 05/29/2014 12:50 PM, Peter Zijlstra wrote:
>> > 
>> > 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.. 

Oh, my bad, I thought you referred to the mutex lock in sync_child_event().


Thanks,
Sasha