perf header: Make build_cpu_topology skip offline/absent CPUs

When build_cpu_topo() encounters offline/absent CPUs, it fails to find any
sysfs entries and returns failure.

This leads to build_cpu_topology() and write_cpu_topology() failing as
well.

Because HEADER_CPU_TOPOLOGY has not been written, read leaves cpu_topology_map
NULL and we get NULL ptr deref at:

  ...
   cmd_test
    __cmd_test
     test_and_print
      run_test
       test_session_topology
        check_cpu_topology

  36: Session topology                           :
  --- start ---
  test child forked, pid 14902
  templ file: /tmp/perf-test-4CKocW
  failed to write feature HEADER_CPU_TOPOLOGY
  perf: Segmentation fault
  Obtained 9 stack frames.
  ./perf(sighandler_dump_stack+0x41) [0x5095f1]
  /lib64/libc.so.6(+0x35250) [0x7f4b7c3c9250]
  ./perf(test_session_topology+0x1db) [0x490ceb]
  ./perf() [0x475b68]
  ./perf(cmd_test+0x5b9) [0x4763c9]
  ./perf() [0x4945a3]
  ./perf(main+0x69f) [0x427e8f]
  /lib64/libc.so.6(__libc_start_main+0xf5) [0x7f4b7c3b5b35]
  ./perf() [0x427fb9]
  test child interrupted
  ---- end ----
  Session topology: FAILED!

This patch makes build_cpu_topology() skip offline/absent CPUs, by checking
their presence against cpu_map built from online CPUs.

Signed-off-by: Jan Stancek <jstancek@redhat.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/a271b770175524f4961d4903af33798358a4a518.1487146877.git.jstancek@redhat.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

1 files changed, 16 insertions, 3 deletions

diff --git a/tools/perf/util/header.c b/tools/perf/util/header.c
index 3d12c16e5103..1222f6c5e7b3 100644
--- a/tools/perf/util/header.c
+++ b/tools/perf/util/header.c
@@ -505,24 +505,31 @@ static void free_cpu_topo(struct cpu_topo *tp)
 
 static struct cpu_topo *build_cpu_topology(void)
 {
-        struct cpu_topo *tp;
+        struct cpu_topo *tp = NULL;
         void *addr;
         u32 nr, i;
         size_t sz;
         long ncpus;
         int ret = -1;
+        struct cpu_map *map;
 
         ncpus = sysconf(_SC_NPROCESSORS_CONF);
         if (ncpus < 0)
                 return NULL;
 
+        /* build online CPU map */
+        map = cpu_map__new(NULL);
+        if (map == NULL) {
+                pr_debug("failed to get system cpumap\n");
+                return NULL;
+        }
+
         nr = (u32)(ncpus & UINT_MAX);
 
         sz = nr * sizeof(char *);
-
         addr = calloc(1, sizeof(*tp) + 2 * sz);
         if (!addr)
-                return NULL;
+                goto out_free;
 
         tp = addr;
         tp->cpu_nr = nr;
@@ -532,10 +539,16 @@ static struct cpu_topo *build_cpu_topology(void)
         tp->thread_siblings = addr;
 
         for (i = 0; i < nr; i++) {
+                if (!cpu_map__has(map, i))
+                        continue;
+
                 ret = build_cpu_topo(tp, i);
                 if (ret < 0)
                         break;
         }
+
+out_free:
+        cpu_map__put(map);
         if (ret) {
                 free_cpu_topo(tp);
                 tp = NULL;