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Date: Wed, 20 May 2015 08:58:23 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Alexei Starovoitov <ast@plumgrid.com>
Cc: Ingo Molnar <mingo@kernel.org>,
        Arnaldo Carvalho de Melo <acme@infradead.org>,
        Wang Nan <wangnan0@huawei.com>, lizefan@huawei.com, pi3orama@163.com,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH tip] perf/events/core: fix race in bpf program unregister
Message-ID: <20150520065823.GJ3644@twins.programming.kicks-ass.net>
References: <1431717321-28772-1-git-send-email-ast@plumgrid.com>
 <555C1B29.1070404@plumgrid.com>
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On Tue, May 19, 2015 at 10:27:05PM -0700, Alexei Starovoitov wrote:
> On 5/15/15 12:15 PM, Alexei Starovoitov wrote:
> >there is a race between perf_event_free_bpf_prog() and free_trace_kprobe():
> >
> >__free_event()
> >   event->destroy(event)
> >     tp_perf_event_destroy()
> >       perf_trace_destroy()
> >         perf_trace_event_unreg()
> >
> >which is dropping event->tp_event->perf_refcount and allows to proceed in:
> >
> >unregister_trace_kprobe()
> >   unregister_kprobe_event()
> >       trace_remove_event_call()
> >             probe_remove_event_call()
> >free_trace_kprobe()
> >
> >while __free_event does:
> >call_rcu(&event->rcu_head, free_event_rcu);
> >   free_event_rcu()
> >     perf_event_free_bpf_prog()
> >
> >To fix the race simply move perf_event_free_bpf_prog() before
> >event->destroy(), since event->tp_event is still valid at that point.
> >
> >Note, perf_trace_destroy() is not racing with trace_remove_event_call()
> >since they both grab event_mutex.
> >
> >Fixes: 2541517c32be ("tracing, perf: Implement BPF programs attached to kprobes")
> >Reported-by: Wang Nan <wangnan0@huawei.com>
> >Signed-off-by: Alexei Starovoitov <ast@plumgrid.com>
> 
> ping.
> This is needed in 4.1.

Thanks, queued for perf/urgent.