[PATCH 07/23] perf stat: Avoid sending SIGTERM to random processes

From: Arnaldo Carvalho de Melo
Date: Wed Jul 10 2013 - 15:24:47 EST


From: Stephane Eranian <eranian@xxxxxxxxxx>

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@xxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/20130604154426.GA2928@quad
Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
---
tools/perf/builtin-stat.c | 23 ++++++++++++++++++++++-
1 file changed, 22 insertions(+), 1 deletion(-)

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 int run_count = 1;
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 @@ static void skip_signal(int signo)
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;

--
1.8.1.4

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