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 <[email protected]>
---
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;
Any comment on this patch Arnaldo?
On Tue, Jun 4, 2013 at 5:44 PM, Stephane Eranian <[email protected]> wrote:
>
> 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 <[email protected]>
> ---
>
> 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;
>
Commit-ID: d07f0b120642f442d81a61f68a9325fb7717004f
Gitweb: http://git.kernel.org/tip/d07f0b120642f442d81a61f68a9325fb7717004f
Author: Stephane Eranian <[email protected]>
AuthorDate: Tue, 4 Jun 2013 17:44:26 +0200
Committer: Arnaldo Carvalho de Melo <[email protected]>
CommitDate: Mon, 8 Jul 2013 17:36:33 -0300
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 <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: Namhyung Kim <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Link: http://lkml.kernel.org/r/20130604154426.GA2928@quad
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>
---
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;