Commit dead9f29 authored May 15, 2015 by Alexei Starovoitov Committed by Ingo Molnar May 27, 2015

perf: Fix race in BPF program unregister



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.

Reported-by: Wang Nan <wangnan0@huawei.com>
Signed-off-by: Alexei Starovoitov <ast@plumgrid.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Arnaldo Carvalho de Melo <acme@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: lizefan@huawei.com
Cc: pi3orama@163.com
Fixes: 2541517c ("tracing, perf: Implement BPF programs attached to kprobes")
Link: http://lkml.kernel.org/r/1431717321-28772-1-git-send-email-ast@plumgrid.com


Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent ba155e2d

kernel/events/core.c

+2 −1

Original line number	Diff line number	Diff line
		@@ -3442,7 +3442,6 @@ static void free_event_rcu(struct rcu_head *head)
		if (event->ns)
		put_pid_ns(event->ns);
		perf_event_free_filter(event);
		perf_event_free_bpf_prog(event);
		kfree(event);
		}

		@@ -3573,6 +3572,8 @@ static void __free_event(struct perf_event *event)
		put_callchain_buffers();
		}

		perf_event_free_bpf_prog(event);

		if (event->destroy)
		event->destroy(event);

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