tracing: Fix sched switch start/stop refcount racy updates
commit64ae572bc7
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@vger.kernel.org CC: Steven Rostedt (VMware) <rostedt@goodmis.org> CC: Joel Fernandes (Google) <joel@joelfernandes.org> CC: Peter Zijlstra <peterz@infradead.org> CC: Thomas Gleixner <tglx@linutronix.de> CC: Paul E. McKenney <paulmck@linux.ibm.com> Reported-by: syzbot+774fddf07b7ab29a1e55@syzkaller.appspotmail.com Fixes:d914ba37d7
("tracing: Add support for recording tgid of tasks") Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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@ -89,8 +89,10 @@ static void tracing_sched_unregister(void)
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static void tracing_start_sched_switch(int ops)
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{
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bool sched_register = (!sched_cmdline_ref && !sched_tgid_ref);
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bool sched_register;
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mutex_lock(&sched_register_mutex);
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sched_register = (!sched_cmdline_ref && !sched_tgid_ref);
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switch (ops) {
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case RECORD_CMDLINE:
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