perf machine: Protect the machine->threads with a rwlock

In addition to using refcounts for the struct thread lifetime
management, we need to protect access to machine->threads from
concurrent access.

That happens in 'perf top', where a thread processes events, inserting
and deleting entries from that rb_tree while another thread decays
hist_entries, that end up dropping references and ultimately deleting
threads from the rb_tree and releasing its resources when no further
hist_entry (or other data structures, like in 'perf sched') references
it.

So the rule is the same for refcounts + protected trees in the kernel,
get the tree lock, find object, bump the refcount, drop the tree lock,
return, use object, drop the refcount if no more use of it is needed,
keep it if storing it in some other data structure, drop when releasing
that data structure.

I.e. pair "t = machine__find(new)_thread()" with a "thread__put(t)", and
"perf_event__preprocess_sample(&al)" with "addr_location__put(&al)".

The addr_location__put() one is because as we return references to
several data structures, we may end up adding more reference counting
for the other data structures and then we'll drop it at
addr_location__put() time.

Acked-by: David Ahern <dsahern@gmail.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Borislav Petkov <bp@suse.de>
Cc: Don Zickus <dzickus@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/n/tip-bs9rt4n0jw3hi9f3zxyy3xln@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

1 files changed, 14 insertions, 8 deletions

diff --git a/tools/perf/tests/code-reading.c b/tools/perf/tests/code-reading.c
index ca0e480e741b..e2a432b67d52 100644
--- a/tools/perf/tests/code-reading.c
+++ b/tools/perf/tests/code-reading.c
@@ -248,6 +248,7 @@ static int process_sample_event(struct machine *machine,
         struct perf_sample sample;
         struct thread *thread;
         u8 cpumode;
+        int ret;
 
         if (perf_evlist__parse_sample(evlist, event, &sample)) {
                 pr_debug("perf_evlist__parse_sample failed\n");
@@ -262,7 +263,9 @@ static int process_sample_event(struct machine *machine,
 
         cpumode = event->header.misc & PERF_RECORD_MISC_CPUMODE_MASK;
 
-        return read_object_code(sample.ip, READLEN, cpumode, thread, state);
+        ret = read_object_code(sample.ip, READLEN, cpumode, thread, state);
+        thread__put(thread);
+        return ret;
 }
 
 static int process_event(struct machine *machine, struct perf_evlist *evlist,
@@ -457,13 +460,13 @@ static int do_test_code_reading(bool try_kcore)
         thread = machine__findnew_thread(machine, pid, pid);
         if (!thread) {
                 pr_debug("machine__findnew_thread failed\n");
-                goto out_err;
+                goto out_put;
         }
 
         cpus = cpu_map__new(NULL);
         if (!cpus) {
                 pr_debug("cpu_map__new failed\n");
-                goto out_err;
+                goto out_put;
         }
 
         while (1) {
@@ -472,7 +475,7 @@ static int do_test_code_reading(bool try_kcore)
                 evlist = perf_evlist__new();
                 if (!evlist) {
                         pr_debug("perf_evlist__new failed\n");
-                        goto out_err;
+                        goto out_put;
                 }
 
                 perf_evlist__set_maps(evlist, cpus, threads);
@@ -485,7 +488,7 @@ static int do_test_code_reading(bool try_kcore)
                 ret = parse_events(evlist, str, NULL);
                 if (ret < 0) {
                         pr_debug("parse_events failed\n");
-                        goto out_err;
+                        goto out_put;
                 }
 
                 perf_evlist__config(evlist, &opts);
@@ -506,7 +509,7 @@ static int do_test_code_reading(bool try_kcore)
                                 continue;
                         }
                         pr_debug("perf_evlist__open failed\n");
-                        goto out_err;
+                        goto out_put;
                 }
                 break;
         }
@@ -514,7 +517,7 @@ static int do_test_code_reading(bool try_kcore)
         ret = perf_evlist__mmap(evlist, UINT_MAX, false);
         if (ret < 0) {
                 pr_debug("perf_evlist__mmap failed\n");
-                goto out_err;
+                goto out_put;
         }
 
         perf_evlist__enable(evlist);
@@ -525,7 +528,7 @@ static int do_test_code_reading(bool try_kcore)
 
         ret = process_events(machine, evlist, &state);
         if (ret < 0)
-                goto out_err;
+                goto out_put;
 
         if (!have_vmlinux && !have_kcore && !try_kcore)
                 err = TEST_CODE_READING_NO_KERNEL_OBJ;
@@ -535,7 +538,10 @@ static int do_test_code_reading(bool try_kcore)
                 err = TEST_CODE_READING_NO_ACCESS;
         else
                 err = TEST_CODE_READING_OK;
+out_put:
+        thread__put(thread);
 out_err:
+
         if (evlist) {
                 perf_evlist__delete(evlist);
         } else {