perf tools: Lock to protect comm_str rb tree

perf tools: Lock to protect comm_str rb tree

Add comm_str_lock to protect comm_str rb tree.

The lock is only needed for multithreaded code, so using mutex wrappers
provided by perf tool.

Signed-off-by: Kan Liang <[email protected]>
Acked-by: Jiri Olsa <[email protected]>
Cc: Adrian Hunter <[email protected]>
Cc: Alexei Starovoitov <[email protected]>
Cc: Andi Kleen <[email protected]>
Cc: He Kuang <[email protected]>
Cc: Lukasz Odzioba <[email protected]>
Cc: Namhyung Kim <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Wang Nan <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>