linux-kernel - [PATCH 5.4 027/309] tracing: Fix sched switch start/stop refcount racy updates

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Date:   Mon, 10 Feb 2020 04:29:43 -0800
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        "Steven Rostedt (VMware)" <rostedt@...dmis.org>,
        "Joel Fernandes (Google)" <joel@...lfernandes.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Paul E. McKenney" <paulmck@...ux.ibm.com>,
        syzbot+774fddf07b7ab29a1e55@...kaller.appspotmail.com,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Subject: [PATCH 5.4 027/309] tracing: Fix sched switch start/stop refcount racy updates

From: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>

commit 64ae572bc7d0060429e40e1c8d803ce5eb31a0d6 upstream.

Reading the sched_cmdline_ref and sched_tgid_ref initial state within
tracing_start_sched_switch without holding the sched_register_mutex is
racy against concurrent updates, which can lead to tracepoint probes
being registered more than once (and thus trigger warnings within
tracepoint.c).

[ May be the fix for this bug ]
Link: https://lore.kernel.org/r/000000000000ab6f84056c786b93@google.com

Link: http://lkml.kernel.org/r/20190817141208.15226-1-mathieu.desnoyers@efficios.com

Cc: stable@...r.kernel.org
CC: Steven Rostedt (VMware) <rostedt@...dmis.org>
CC: Joel Fernandes (Google) <joel@...lfernandes.org>
CC: Peter Zijlstra <peterz@...radead.org>
CC: Thomas Gleixner <tglx@...utronix.de>
CC: Paul E. McKenney <paulmck@...ux.ibm.com>
Reported-by: syzbot+774fddf07b7ab29a1e55@...kaller.appspotmail.com
Fixes: d914ba37d7145 ("tracing: Add support for recording tgid of tasks")
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 kernel/trace/trace_sched_switch.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/kernel/trace/trace_sched_switch.c
+++ b/kernel/trace/trace_sched_switch.c
@@ -89,8 +89,10 @@ static void tracing_sched_unregister(voi

 static void tracing_start_sched_switch(int ops)
 {
-	bool sched_register = (!sched_cmdline_ref && !sched_tgid_ref);
+	bool sched_register;
+
 	mutex_lock(&sched_register_mutex);
+	sched_register = (!sched_cmdline_ref && !sched_tgid_ref);

 	switch (ops) {
 	case RECORD_CMDLINE: