[PATCH] perf stat: avoid sending SIGTERM to random processes

[PATCH] perf stat: avoid sending SIGTERM to random processes

[Stephane Eranian]

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>
---

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;
 

Re: [PATCH] perf stat: avoid sending SIGTERM to random processes

[Stephane Eranian]

Any comment on this patch Arnaldo?


On Tue, Jun 4, 2013 at 5:44 PM, Stephane Eranian <eranian@google.com> 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 <eranian@google.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 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;
>

[tip:perf/urgent] perf stat: Avoid sending SIGTERM to random processes

[tip-bot for Stephane Eranian]

Commit-ID:  d07f0b120642f442d81a61f68a9325fb7717004f
Gitweb:     http://git.kernel.org/tip/d07f0b120642f442d81a61f68a9325fb7717004f
Author:     Stephane Eranian <eranian@google.com>
AuthorDate: Tue, 4 Jun 2013 17:44:26 +0200
Committer:  Arnaldo Carvalho de Melo <acme@redhat.com>
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 <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>
---
 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;