librdmacm: fix race in ucma_init()

librdmacm: fix race in ucma_init()

There's a potential race with ucma_init() and calls that check whether
the library is ready for use.  For example, in rdma_create_id, this
check is performed:

	hr = cma_dev_cnt ? 0 : ucma_init();
	if (hr) {
		return hr;
	}

Since the check for cma_dev_cnt is outside of any synchronization, if it
is non-zeroy, then the code will assume that initialization is complete.
However, ucma_init() can set cma_dev_cnt to non-zeroy before it has finished
executing.  The full impact of this race is unknown, but it can't be good.
In the worst case, the application may crash.

Fix this by ensuring that all initialization is complete before cma_dev_cnt
is incremented.  Note that ucma_init() provides synchronization to protect
against duplicate threads handling init.  The cma_dev_cnt check is used to
avoid synchronization on multiple calls into the library after initialization.

Signed-off-by: Sean Hefty <sean.hefty@intel.com>
git-svn-id: svn://openib.tc.cornell.edu/gen1@2383 ad392aa1-c5ef-ae45-8dd8-e69d62a5ef86