[PATCH 1/8] perf header: Fix segfault on build_mem_topology() error path

[Adrian Hunter <adrian.hunter@intel.com>]

Do not increase the node count unless a node has been successfully read,
because it can lead to a segfault if an error occurs.

For example, if perf exceeds the open file limit in memory_node__read(),
which, on a test system, could be made to happen by setting the file limit
to exactly 32:

 Before:

  $ ulimit -n 32
  $ perf mem record --all-user -- sleep 1
  [ perf record: Woken up 1 times to write data ]
  failed: can't open memory sysfs data
  perf: Segmentation fault
  Obtained 14 stack frames.
  perf(sighandler_dump_stack+0x48) [0x55f4b1f59558]
  /lib/x86_64-linux-gnu/libc.so.6(+0x42520) [0x7f4ba1c42520]
  /lib/x86_64-linux-gnu/libc.so.6(free+0x1e) [0x7f4ba1ca53fe]
  perf(+0x178ff4) [0x55f4b1f48ff4]
  perf(+0x179a70) [0x55f4b1f49a70]
  perf(+0x17ef5d) [0x55f4b1f4ef5d]
  perf(+0x85c0b) [0x55f4b1e55c0b]
  perf(cmd_record+0xe1d) [0x55f4b1e5920d]
  perf(cmd_mem+0xc96) [0x55f4b1e80e56]
  perf(+0x130460) [0x55f4b1f00460]
  perf(main+0x689) [0x55f4b1e427d9]
  /lib/x86_64-linux-gnu/libc.so.6(+0x29d90) [0x7f4ba1c29d90]
  /lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0x80) [0x7f4ba1c29e40]
  perf(_start+0x25) [0x55f4b1e42a25]
  Segmentation fault (core dumped)
  $

After:

  $ ulimit -n 32
  $ perf mem record --all-user -- sleep 1
  [ perf record: Woken up 1 times to write data ]
  failed: can't open memory sysfs data
  [ perf record: Captured and wrote 0.005 MB perf.data (11 samples) ]
  $

Fixes: f8e502b9d1b3 ("perf header: Ensure bitmaps are freed")
Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
---
 tools/perf/util/header.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/tools/perf/util/header.c b/tools/perf/util/header.c
index 1c687b5789c0..08cc2febabde 100644
--- a/tools/perf/util/header.c
+++ b/tools/perf/util/header.c
@@ -1444,7 +1444,9 @@ static int build_mem_topology(struct memory_node **nodesp, u64 *cntp)
 			nodes = new_nodes;
 			size += 4;
 		}
-		ret = memory_node__read(&nodes[cnt++], idx);
+		ret = memory_node__read(&nodes[cnt], idx);
+		if (!ret)
+			cnt += 1;
 	}
 out:
 	closedir(dir);
-- 
2.34.1