On Thu, Nov 11, 2021 at 08:26:58AM +0100, Paolo Bonzini wrote:

On 11/11/21 03:07, Sean Christopherson wrote:

quoted

  EXPORT_SYMBOL_GPL(perf_register_guest_info_callbacks);
  int perf_unregister_guest_info_callbacks(struct perf_guest_info_callbacks *cbs)
  {
-	perf_guest_cbs = NULL;
+	if (WARN_ON_ONCE(rcu_access_pointer(perf_guest_cbs) != cbs))
+		return -EINVAL;
+
+	rcu_assign_pointer(perf_guest_cbs, NULL);
+	synchronize_rcu();

This technically could be RCU_INIT_POINTER but it's not worth a respin.
There are dozens of other occurrences, and if somebody wanted they
could use Coccinelle to fix all of them.

I've been pushing the other way, trying to get rid of RCU_INIT_POINTER()
since rcu_assign_pointer(, NULL) actualy DTRT per __builtin_constant_p()
etc.

There's a very few sites where we use RCU_INIT_POINTER() with a !NULL
argument, and those are 'special'.

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