perf stat: Avoid sending SIGTERM to random processes
This patch fixes a problem with perf stat whereby on termination it may
send a SIGTERM signal to random processes on systems with high PID
recycling. I got some actual bug reports on this.
There is race between the SIGCHLD and sig_atexit() handlers. This patch
addresses this problem by clearing child_pid in the SIGCHLD handler.
Signed-off-by: Stephane Eranian <eranian@google.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20130604154426.GA2928@quad
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
diff --git a/tools/perf/builtin-stat.c b/tools/perf/builtin-stat.c
index 7e910ba..95768af 100644
--- a/tools/perf/builtin-stat.c
+++ b/tools/perf/builtin-stat.c
@@ -87,7 +87,7 @@
static bool no_inherit = false;
static bool scale = true;
static enum aggr_mode aggr_mode = AGGR_GLOBAL;
-static pid_t child_pid = -1;
+static volatile pid_t child_pid = -1;
static bool null_run = false;
static int detailed_run = 0;
static bool big_num = true;
@@ -1148,13 +1148,34 @@
done = 1;
signr = signo;
+ /*
+ * render child_pid harmless
+ * won't send SIGTERM to a random
+ * process in case of race condition
+ * and fast PID recycling
+ */
+ child_pid = -1;
}
static void sig_atexit(void)
{
+ sigset_t set, oset;
+
+ /*
+ * avoid race condition with SIGCHLD handler
+ * in skip_signal() which is modifying child_pid
+ * goal is to avoid send SIGTERM to a random
+ * process
+ */
+ sigemptyset(&set);
+ sigaddset(&set, SIGCHLD);
+ sigprocmask(SIG_BLOCK, &set, &oset);
+
if (child_pid != -1)
kill(child_pid, SIGTERM);
+ sigprocmask(SIG_SETMASK, &oset, NULL);
+
if (signr == -1)
return;