Description of problem:
When running 'perf top, and the number of event record is zero, 
press ENTER key, then perf command terminates with segfault.

The patch to fix this issue has already been posted, and was merged in the stock kernel v3.4.

  [tip:perf/core] perf hists browser: Fix NULL deref in hists browsing code
  https://lkml.org/lkml/2012/4/13/305

This patch isn't applied to perf-2.6.32-279.2.1.el6(07/25/2012 latest).
Please backport this patch.

Version-Release number of selected component (if applicable):


How reproducible:
every time when the number of event record is zero.

Steps to Reproduce:
# perf top -e syscalls:sys_enter_sendmsg   <--- sys_xxx_xxxxx can be anything.

  <<< press ENTER key >>>

perf: Segmentation fault
#

  
Actual results:
perf top tui crash

Expected results:
perf command terminates normally without segfault.

Additional info:
# rpm -q kernel perf
kernel-2.6.32-279.el6.x86_64
perf-2.6.32-279.el6.x86_64
# gdb -q perf
Reading symbols from /usr/bin/perf...Reading symbols from /usr/lib/debug/usr/bin/perf.debug...done.
done.
(gdb) run top -e syscalls:sys_enter_sendmsg
Starting program: /usr/bin/perf top -e syscalls:sys_enter_sendmsg
[Thread debugging using libthread_db enabled]

                                                     [New Thread 0x7ffff1129700 (LWP 44119)]

Events: 0  syscalls:sys_enter_sendmsg

  <<< press ENTER key >>>

Program received signal SIGSEGV, Segmentation fault.
[Switching to Thread 0x7ffff1129700 (LWP 44119)]
hist_browser__toggle_fold (evsel=0xab4c50, nr_events=1, helpline=<value optimized out>,
    ev_name=0xab3220 "syscalls:sys_enter_sendmsg", left_exits=false, timer=0x41f1a0 <perf_top__sort_new_samples>,
    arg=0x7fffffffd700, delay_secs=2) at util/ui/browsers/hists.c:191
191             if (map_symbol__toggle_fold(self->selection)) {
Missing separate debuginfos, use: debuginfo-install elfutils-libelf-0.152-1.el6.x86_64 glibc-2.12-1.80.el6.x86_64 newt-0.52.11-3.el6.x86_64 nss-softokn-freebl-3.12.9-11.el6.x86_64 perl-libs-5.10.1-127.el6.x86_64 python-libs-2.6.6-29.el6_2.2.x86_64 slang-2.2.1-1.el6.x86_64
(gdb) bt
#0  hist_browser__toggle_fold (evsel=0xab4c50, nr_events=1, helpline=<value optimized out>,
    ev_name=0xab3220 "syscalls:sys_enter_sendmsg", left_exits=false, timer=0x41f1a0 <perf_top__sort_new_samples>,
    arg=0x7fffffffd700, delay_secs=2) at util/ui/browsers/hists.c:191
#1  hist_browser__run (evsel=0xab4c50, nr_events=1, helpline=<value optimized out>,
    ev_name=0xab3220 "syscalls:sys_enter_sendmsg", left_exits=false, timer=0x41f1a0 <perf_top__sort_new_samples>,
    arg=0x7fffffffd700, delay_secs=2) at util/ui/browsers/hists.c:364
#2  perf_evsel__hists_browse (evsel=0xab4c50, nr_events=1, helpline=<value optimized out>,
    ev_name=0xab3220 "syscalls:sys_enter_sendmsg", left_exits=false, timer=0x41f1a0 <perf_top__sort_new_samples>,
    arg=0x7fffffffd700, delay_secs=2) at util/ui/browsers/hists.c:883
#3  0x0000000000471b34 in perf_evlist__tui_browse_hists (evlist=0xab33c0,
    help=0x488b60 "For a higher level overview, try: perf top --sort comm,dso", timer=0x41f1a0 <perf_top__sort_new_samples>,
    arg=0x7fffffffd700, delay_secs=2) at util/ui/browsers/hists.c:1254
#4  0x000000000041f6e4 in display_thread_tui (arg=0x7fffffffd700) at builtin-top.c:544
#5  0x0000003cf9007851 in start_thread () from /lib64/libpthread.so.0
#6  0x0000003cf84e767d in clone () from /lib64/libc.so.6
(gdb) p self
$1 = (struct hist_browser *) 0x7fffec0008c0
(gdb) p self->selection
$2 = (struct map_symbol *) 0x0
(gdb) q
A debugging session is active.ings

        Inferior 1 [process 44116] will be killed.

Quit anyway? (y or n) y
#