perf top: Expand the range of multithreaded phase

In __cmd_top(), perf_set_multithreaded() is used to enable
pthread_rwlock, thus down_read() and down_write () are not nops,
handling concurrency problems

Then 'perf top' uses perf_set_singlethreaded(), switching to the single
threaded phase, assuming that no thread concurrency will happen later.

However, a use after free problem could occur in the single threaded
phase, the concurrent procedure is this:

display_thread                              process_thread
--------------                              --------------
thread__comm_len
  -> thread__comm_str
    -> __thread__comm_str(thread)
                                            thread__delete
                                             -> comm__free
                                              -> comm_str__put
                                               -> zfree(&cs->str)
    -> thread->comm_len = strlen(comm);

Since in single thread phase, perf_singlethreaded is true, down_read()
and down_write() do nothing to avoid concurrency problems.

This patch moves the perf_set_singlethreaded() call to the function tail
to expand the multithreaded phase range, making display_thread() and
process_thread() concurrency safe.

Reviewed-by: Yunfeng Ye <[email protected]>
Signed-off-by: Hangliang Lai  <[email protected]>
Co-developed-by: Wenyu Liu <[email protected]>
Acked-by: Namhyung Kim <[email protected]>
Cc: Adrian Hunter <[email protected]>
Cc: Alexander Shishkin <[email protected]>
Cc: Christian Brauner <[email protected]>
Cc: Feilong Lin <[email protected]>
Cc: Hewenliang <[email protected]>
Cc: Ian Rogers <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: Mark Rutland <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>

diff --git a/tools/perf/builtin-top.c b/tools/perf/builtin-top.c
index 3162bad0d17d25254f47af5668be5262e19e53d4..5d448c36ed22b8917ba46f639381ecf9a167842b 100644 (file)
--- a/tools/perf/builtin-top.c
+++ b/tools/perf/builtin-top.c
@@ -1276,8 +1276,7 @@ static int __cmd_top(struct perf_top *top)
                                    top->evlist->core.threads, true, false,
                                    top->nr_threads_synthesize);
 
-       if (top->nr_threads_synthesize > 1)
-               perf_set_singlethreaded();
+       perf_set_multithreaded();
 
        if (perf_hpp_list.socket) {
                ret = perf_env__read_cpu_topology_map(&perf_env);
@@ -1355,6 +1354,7 @@ out_join:
 out_join_thread:
        cond_signal(&top->qe.cond);
        pthread_join(thread_process, NULL);
+       perf_set_singlethreaded();
        return ret;
 }