linux-kernel - [for-next][PATCH 03/21] tracing: Fix sched switch start/stop refcount racy updates

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Message-Id: <20200130144810.669688514@goodmis.org>
Date:   Thu, 30 Jan 2020 09:47:46 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     linux-kernel@...r.kernel.org
Cc:     Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        stable@...r.kernel.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: [for-next][PATCH 03/21] tracing: Fix sched switch start/stop refcount racy updates

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

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

diff --git a/kernel/trace/trace_sched_switch.c b/kernel/trace/trace_sched_switch.c
index e288168661e1..e304196d7c28 100644
--- a/kernel/trace/trace_sched_switch.c
+++ b/kernel/trace/trace_sched_switch.c
@@ -89,8 +89,10 @@ static void tracing_sched_unregister(void)
 
 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:
-- 
2.24.1