Re: [Qemu-devel] [PATCH] memory: unregister AddressSpace MemoryListener within BQL

[Paolo Bonzini]

On 11/02/2015 06:13, Michael Roth wrote:
> (gdb) print node
> $1 = (struct rcu_head *) 0x11189a68
> (gdb) print node->func
> $2 = (RCUCBFunc *) 0x0
> (gdb) print node->next
> $3 = (struct rcu_head *) 0x3fff9800d4f0
> 
> I've seen it on both x86 and pseries (with spapr hotplug patches applied), and
> have only seen it occur at this spot.
> 
> AFAICT node->func is only set via 1 of:
> 
>   call_rcu(old_view, flatview_unref, rcu);
>   call_rcu(as, do_address_space_destroy, rcu);
> 
> so it shouldn't ever be NULL... and there's a wmb after node->func is set,
> prior to the node being made available to the RCU thread via enqueue(), so
> that doesn't seem to be the issue.
> 
> I think the node in this case is a FlatView*, if that helps narrow it down:
> 
> (gdb) print ((AddressSpace *)(0x3fff9800d4f0))->name
> $5 = 0x100000000 <Address 0x100000000 out of bounds>

This is node->next, not node.  The weird address looks almost like node
== &dummy.  I'll try to reproduce.

Paolo