quoted

  Concurrency between readers and writers are handled by the intrinsic
properties of the concurrent radix tree. Concurrency between the tree
initialization which is done asynchronously with readers and writers access
is handled via an atomic variable (revmap_trees_allocated) set when the
tree has been initialized and checked before any reader or writer access
just like we used to check for tree.gfp_mask != 0 before.

Hmm, RCU radix tree is in mainline too for quite a while. I thought
Ben had already converted this code over ages ago...

Nothing against the -rt patch, but mainline should probably be updated
to use RCU as well?

No, I haven't updated that code yet, and yes, we should do it :-)

Cheers,
Ben.