Re: [RFC v4 2/3] memory: add depth assert in address_space_to_flatview

[Peter Xu]

Hi, Paolo,

On Fri, Dec 23, 2022 at 04:47:57PM +0100, Paolo Bonzini wrote:
> On 12/23/22 15:23, Chuang Xu wrote:
> >   static inline FlatView *address_space_to_flatview(AddressSpace *as)
> >   {
> > +    /*
> > +     * Before using any flatview, sanity check we're not during a memory
> > +     * region transaction or the map can be invalid.  Note that this can
> > +     * also be called during commit phase of memory transaction, but that
> > +     * should also only happen when the depth decreases to 0 first.
> > +     */
> > +    assert(memory_region_transaction_get_depth() == 0 || 
> > rcu_read_locked());
> >       return qatomic_rcu_read(&as->current_map);
> >   }
> 
> This is not valid because the transaction could happen in *another* thread.
> In that case memory_region_transaction_depth() will be > 0, but RCU is
> needed.

Do you mean the code is wrong, or the comment?  Note that the code has
checked rcu_read_locked() where introduced in patch 1, but maybe something
else was missed?

Thanks,

-- 
Peter Xu