generic ipi function calls: wait on alloc failure fallback

When a GFP_ATOMIC allocation fails, it falls back to allocating the data on the stack and converting it to a waiting call.

Make sure we actually wait in this case.

---
kernel/smp.c | 1 +

1 file changed, 1 insertion(+)

===================================================================

@@ -312,6 +312,7 @@ int smp_call_function_mask(cpumask_t mas

	if (!data) {
		data = &d;
		data->csd.flags = CSD_FLAG_WAIT;
+		wait = 1;
	}

	spin_lock_init(&data->lock);

cool, thanks!

does this explain the xen64 weirdnesses you've been seeing?

Ingo

No, but I haven't seen it lately. I think the other RCU fixes may have helped. But it's all a bit of a worry: I didn't have a good theory about what was going wrong, the RCU patches didn't look like they'd fix the symptoms I was seeing.

I've seen it with 32 and 64-bit Xen, but there's nothing about the problem which makes me think it's really Xen specific. If it were, I'd expect to see failures all over the place, rather than in just in this one specific place.

I'm concerned there's a lurking bug, particularly if it's a generic race or something that happens to be triggered when running under Xen because of the timing changes. I've tried reproducing it in a hvm Xen domain (so it's running the normal x86 kernel fully virtualized, but with the Xen scheduler, etc). I didn't see a problem, but it isn't a very convincing test one way or the other.

J

ok. I doubt there's much we can do at this stage - the code looks fine. If it's some recently added core kernel problem sooner or later some workload or hw will come about that shows it in a more debuggable manner.

Ingo

Yep. It has been rock solid for me lately, even doing traditionally bug-inducing things like save/restore.

J