perf stat: avoid sending SIGTERM to random processes

PATCH In review Stephane Eranian 2 participants 3 messages Jun 4, 2013 – Jul 12, 2013 perf events

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Stephane Eranian

author

2013-06-04 15:44 UTC #0 lore raw

PATCH 1/1 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]>

---

tools/perf/builtin-stat.c +22 -1

index 7e910ba..95768af 100644
@@ -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;

Stephane Eranian

author

2013-06-19 06:47 UTC #1 lore raw

Any comment on this patch Arnaldo?

Quoted 60 lines · 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 <[email protected]>

---

tools/perf/builtin-stat.c +22 -1

index 7e910ba..95768af 100644
@@ -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-bot for Stephane Eranian

merge bot

2013-07-12 08:51 UTC #2 lore raw

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

In reply to Stephane Eranian

perf stat: Avoid sending SIGTERM to random processes

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 open here

Signed-off-by Arnaldo Carvalho de Melo <[email protected]>

---
 tools/perf/builtin-stat.c | 23 ++++++++++++++++++++++-
 1 file changed, 22 insertions(+), 1 deletion(-)

tools/perf/builtin-stat.c +22 -1

index 7e910ba..95768af 100644
@@ -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;