Mesa expects to be able to map the same buffer, without unmapping it. This leads to problem on long-running program.
On the other hand, libdrm uses cpu_map_count as a refcount and expects its value to decrease so it can unmap buffers.
The previoulsy proprosed fix (https://patchwork.freedesktop.org/patch/258005/) stopped increased the counter when it went past INT_MAX.
This commit instead proposes to use a larger type to store cpu_map_count. The outcome is the same: long running apps will not crash, only the implementation differs.
Closes: mesa#1423 (closed)