perf report: Fix crash showing warning related to kernel maps
perf report: Fix crash showing warning related to kernel maps

While testing https://lkml.org/lkml/2012/4/10/123 I hit this crash:

(gdb) bt
 0  0x000000000042000f in __cmd_report (rep=0x7fff80cec580) at builtin-report.c:380
 1  cmd_report (argc=0, argv=<optimized out>, prefix=<optimized out>) at builtin-report.c:759
 2  0x0000000000414513 in run_builtin (p=0x7724a8, argc=3, argv=0x7fff80ceca70) at perf.c:273
 3  0x0000000000413d41 in handle_internal_command (argv=0x7fff80ceca70, argc=3) at perf.c:345
 4  run_argv (argv=0x7fff80cec880, argcp=0x7fff80cec88c) at perf.c:389
 5  main (argc=3, argv=0x7fff80ceca70) at perf.c:487

kernel_map can be NULL, so need to handle it while dumping a warning
to user.

v2:
- fixed RB_EMPTY_ROOT check -- desc takes the altnerative output when RB_EMPTY_ROOT is false.

Signed-off-by: David Ahern <b80c1600f604d3b0d768f26f90a76757e76005dd@gmail.com>
Cc: Ingo Molnar <9dbbbf0688fedc85ad4da37637f1a64b8c718ee2@elte.hu>
Cc: Peter Zijlstra <3fddac958924aef220f202ca567388ddab3f14a8@infradead.org>
Cc: Stephane Eranian <f199ae9781930a5b94b284ca2f471140752002a7@google.com>
Cc: Namhyung Kim <1b20bcb62cf1b100c528e605608922000dc2fc80@lge.com>
Link: http://lkml.kernel.org/r/1334544855-55021-1-git-send-email-b80c1600f604d3b0d768f26f90a76757e76005dd@gmail.com
Signed-off-by: Arnaldo Carvalho de Melo <293abb6b76d7791c0732cc517d38c4b5c734b87f@redhat.com>

TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs