[tip:perf/core] perf hists browser: Fix segfault if use symbol filter in cmdline

[tip-bot for Wang Nan <tipbot@zytor.com>]

Commit-ID:  4938cf0c7a62025bbfbf3db7bcdcc2c33312bedb
Gitweb:     http://git.kernel.org/tip/4938cf0c7a62025bbfbf3db7bcdcc2c33312bedb
Author:     Wang Nan <wangnan0@huawei.com>
AuthorDate: Mon, 7 Dec 2015 02:35:44 +0000
Committer:  Arnaldo Carvalho de Melo <acme@redhat.com>
CommitDate: Mon, 7 Dec 2015 12:02:35 -0300

perf hists browser: Fix segfault if use symbol filter in cmdline

If feed perf a symbol filter in cmdline and the result is empty,
pressing 'Enter' in the hist browser causes crash:

 # ./perf report perf.data   <-- Common mistake for beginners

Then press 'Enter':

 perf: Segmentation fault
 -------- backtrace --------
 /home/wangnan/perf[0x53e578]
 /lib64/libc.so.6(+0x3545f)[0x7f76bafe045f]
 /home/wangnan/perf[0x539dd4]
 /home/wangnan/perf(perf_evlist__tui_browse_hists+0x96)[0x53d216]
 /home/wangnan/perf(cmd_report+0x1b9f)[0x442c7f]
 /home/wangnan/perf[0x47efa2]
 /home/wangnan/perf(main+0x5f5)[0x432fa5]
 /lib64/libc.so.6(__libc_start_main+0xf4)[0x7f76bafccbd4]
 /home/wangnan/perf[0x4330d4]

This is because 'perf.data' is interpreted as a symbol filter, and the
result is empty, so selection is empty. However,
hist_browser__toggle_fold() forgets to check it.

This patch simply return false when selection is NULL.

Signed-off-by: Wang Nan <wangnan0@huawei.com>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Zefan Li <lizefan@huawei.com>
Cc: pi3orama@163.com
Link: http://lkml.kernel.org/r/1449455746-41952-2-git-send-email-wangnan0@huawei.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
---
 tools/perf/ui/browsers/hists.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/tools/perf/ui/browsers/hists.c b/tools/perf/ui/browsers/hists.c
index 84c8251..81def6c3 100644
--- a/tools/perf/ui/browsers/hists.c
+++ b/tools/perf/ui/browsers/hists.c
@@ -298,6 +298,9 @@ static bool hist_browser__toggle_fold(struct hist_browser *browser)
 	struct callchain_list *cl = container_of(ms, struct callchain_list, ms);
 	bool has_children;
 
+	if (!he || !ms)
+		return false;
+
 	if (ms == &he->ms)
 		has_children = hist_entry__toggle_fold(he);
 	else