Ceph

That's odd:

#else
/*
 * crappy slow implementation that uses a pthreads spinlock.
 */
#include "include/Spinlock.h" 

namespace ceph {
  typedef atomic_spinlock_t<unsigned> atomic_t;
  typedef atomic_spinlock_t<unsigned long long> atomic64_t;
}

#endif

definitely specifies atomic_t. Unless it's the nested #ifs:

#ifndef NO_ATOMIC_OPS
[ definition goes here...]
#if SIZEOF_AO_T == 8
  typedef atomic_t atomic64_t;
#else
  typedef atomic_spinlock_t<unsigned long long> atomic64_t;
#endif

}

#else
/*
 * crappy slow implementation that uses a pthreads spinlock.
 */

The internet tells me we can nest them, but that's the only thing I can see that might have broken them.