Re: [PATCH v8 1/5] mm: introduce a common interface for balloonpages mobility

[Peter Zijlstra]

On Tue, 2012-08-21 at 16:52 +0300, Michael S. Tsirkin wrote:
> > +             rcu_read_lock();
> > +             mapping = rcu_dereference(page->mapping);
> > +             if (mapping_balloon(mapping))
> > +                     ret = true;
> > +             rcu_read_unlock();
> 
> This looks suspicious: you drop rcu_read_unlock
> so can't page switch from balloon to non balloon? 

RCU read lock is a non-exclusive lock, it cannot avoid anything like
that.
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