Commit 5bfbcd1e authored by Steven Rostedt's avatar Steven Rostedt Committed by Steven Rostedt (Google)
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tracing/timerlat: Add interface_lock around clearing of kthread in stop_kthread() 

The timerlat interface will get and put the task that is part of the
"kthread" field of the osn_var to keep it around until all references are
released. But here's a race in the "stop_kthread()" code that will call
put_task_struct() on the kthread if it is not a kernel thread. This can
race with the releasing of the references to that task struct and the
put_task_struct() can be called twice when it should have been called just
once.

Take the interface_lock() in stop_kthread() to synchronize this change.
But to do so, the function stop_per_cpu_kthreads() needs to change the
loop from for_each_online_cpu() to for_each_possible_cpu() and remove the
cpu_read_lock(), as the interface_lock can not be taken while the cpu
locks are held. The only side effect of this change is that it may do some
extra work, as the per_cpu variables of the offline CPUs would not be set
anyway, and would simply be skipped in the loop.

Remove unneeded "return;" in stop_kthread().

Cc: stable@vger.kernel.org
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Tomas Glozar <tglozar@redhat.com>
Cc: John Kacur <jkacur@redhat.com>
Cc: "Luis Claudio R. Goncalves" <lgoncalv@redhat.com>
Link: https://lore.kernel.org/20240905113359.2b934242@gandalf.local.home


Fixes: e88ed227 ("tracing/timerlat: Add user-space interface")
Signed-off-by: default avatarSteven Rostedt (Google) <rostedt@goodmis.org>
parent e6a53481

kernel/trace/trace_osnoise.c

+6 −7
Original line number Diff line number Diff line
@@ -1953,8 +1953,12 @@ static void stop_kthread(unsigned int cpu) 
{

	struct task_struct *kthread;



	mutex_lock(&interface_lock);

	kthread = per_cpu(per_cpu_osnoise_var, cpu).kthread;

	if (kthread) {

		per_cpu(per_cpu_osnoise_var, cpu).kthread = NULL;

		mutex_unlock(&interface_lock);



		if (cpumask_test_and_clear_cpu(cpu, &kthread_cpumask) &&

		    !WARN_ON(!test_bit(OSN_WORKLOAD, &osnoise_options))) {

			kthread_stop(kthread);
@@ -1967,8 +1971,8 @@ static void stop_kthread(unsigned int cpu) 
			kill_pid(kthread->thread_pid, SIGKILL, 1);

			put_task_struct(kthread);

		}

		per_cpu(per_cpu_osnoise_var, cpu).kthread = NULL;

	} else {

		mutex_unlock(&interface_lock);

		/* if no workload, just return */

		if (!test_bit(OSN_WORKLOAD, &osnoise_options)) {

			/*
@@ -1976,7 +1980,6 @@ static void stop_kthread(unsigned int cpu) 
			 */

			per_cpu(per_cpu_osnoise_var, cpu).sampling = false;

			barrier();

			return;

		}

	}

}
@@ -1991,12 +1994,8 @@ static void stop_per_cpu_kthreads(void) 
{

	int cpu;



	cpus_read_lock();



	for_each_online_cpu(cpu)

	for_each_possible_cpu(cpu)

		stop_kthread(cpu);



	cpus_read_unlock();

}



/*