perf: Fix race in BPF program unregister
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 <7b589a40e0ecd4816b422e8ed1f74a01c34bf6bb@huawei.com>
Signed-off-by: Alexei Starovoitov <c24c0248770ae98831f8a654310d4c2e07514c61@plumgrid.com>
Signed-off-by: Peter Zijlstra (Intel) <3fddac958924aef220f202ca567388ddab3f14a8@infradead.org>
Cc: Arnaldo Carvalho de Melo <293abb6b76d7791c0732cc517d38c4b5c734b87f@infradead.org>
Cc: Linus Torvalds <69652caca27c8b940640ad396ab71f93cacec34f@linux-foundation.org>
Cc: Peter Zijlstra <3fddac958924aef220f202ca567388ddab3f14a8@infradead.org>
Cc: Thomas Gleixner <00e4cf8f46a57000a44449bf9dd8cbbcc209fd2a@linutronix.de>
Cc: a8167b9d27aca9c6624754deb52c4c6420eded04@huawei.com
Cc: d3a709cba82ff13e91126748cd399b3cb8e95d2e@163.com
Fixes: 2541517c32be ("tracing, perf: Implement BPF programs attached to kprobes")
Link: http://lkml.kernel.org/r/1431717321-28772-1-git-send-email-c24c0248770ae98831f8a654310d4c2e07514c61@plumgrid.com
Signed-off-by: Ingo Molnar <9dbbbf0688fedc85ad4da37637f1a64b8c718ee2@kernel.org>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs