virtgpu_cross_domain: Hold a lock for all of bo_create

In crosvm, the MinigbmDevice implementation of the Gralloc interface
assumes that a call to get_image_memory_requirements will be immediately
followed by a matching call to allocate_memory, as the implementation
stashes a buffer allocated by the first call to be returned by the
second.

However on Android multiple processes/threads can be making calls to
allocate memory via CrosGralloc. In particular if the device is
configured to use the cross-domain back-end, and two threads are trying
to allocate memory, the two requests to get the memory requirements for
an allocation can be submitted to crosvm followed by the two requests to
actually allocate memory.

When the assumption is violated, the crosvm code was raising an error
for the SECOND memory requirement request. However the error does not
propagate back to the virtgpu_cross_domain code here. The result is that
the request is understood to have succeeded, and the code here then
reads the size metadata from the response buffer, but that contains the
values from the FIRST memory requirement request. Those values may be

There is a fix for crosvm in review (https://crrev.com/c/6260975) to
not raise an error if the calls are not made in the expected order,
while still maintaining a single stashed buffer. However this means the
memory allocated for one of the two requests must be released, and would
have to be reallocated, at some extra runtime cost as allocating
graphics memory requires allocating physically contiguous memory.

The existing cross-domain code here acquired a simple mutex lock to
maintain a metadata cache, which was held for the duration of the first
call. This change extends the duration of the lock to the entire
allocation request so that the guest always makes the two requests in
the expected order.

BUG=b:395748805,b:355060470
TEST=ARCVM on Corsola starts up under high CPU stress

Change-Id: I6429ea28141ef440345a3eb442066173b3e04802
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/minigbm/+/6288246
Commit-Queue: Lloyd Pique <lpique@google.com>
Reviewed-by: Yiwei Zhang <zzyiwei@chromium.org>
Tested-by: Lloyd Pique <lpique@google.com>