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Commit 60f53782 authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

rcu: Prevent initialization race in rcutorture kthreads 



When you do something like "t = kthread_run(...)", it is possible that
the kthread will start running before the assignment to "t" happens.
If the child kthread expects to find a pointer to its task_struct in "t",
it will then be fatally disappointed.  This commit therefore switches
such cases to kthread_create() followed by wake_up_process(), guaranteeing
that the assignment happens before the child kthread starts running.

Reported-by: default avatarFengguang Wu <fengguang.wu@intel.com>
Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
parent 2caa1e44

kernel/rcutorture.c

+6 −4
Original line number Original line Diff line number Diff line
@@ -2029,7 +2029,7 @@ rcu_torture_init(void) 
	/* Start up the kthreads. */

	/* Start up the kthreads. */





	VERBOSE_PRINTK_STRING("Creating rcu_torture_writer task");

	VERBOSE_PRINTK_STRING("Creating rcu_torture_writer task");

	writer_task = kthread_run(rcu_torture_writer, NULL,

	writer_task = kthread_create(rcu_torture_writer, NULL,

				     "rcu_torture_writer");

				     "rcu_torture_writer");

	if (IS_ERR(writer_task)) {

	if (IS_ERR(writer_task)) {

		firsterr = PTR_ERR(writer_task);

		firsterr = PTR_ERR(writer_task);
@@ -2037,6 +2037,7 @@ rcu_torture_init(void) 
		writer_task = NULL;

		writer_task = NULL;

		goto unwind;

		goto unwind;

	}

	}

	wake_up_process(writer_task);

	fakewriter_tasks = kzalloc(nfakewriters * sizeof(fakewriter_tasks[0]),

	fakewriter_tasks = kzalloc(nfakewriters * sizeof(fakewriter_tasks[0]),

				   GFP_KERNEL);

				   GFP_KERNEL);

	if (fakewriter_tasks == NULL) {

	if (fakewriter_tasks == NULL) {
@@ -2151,7 +2152,7 @@ rcu_torture_init(void) 
	}

	}

	if (shutdown_secs > 0) {

	if (shutdown_secs > 0) {

		shutdown_time = jiffies + shutdown_secs * HZ;

		shutdown_time = jiffies + shutdown_secs * HZ;

		shutdown_task = kthread_run(rcu_torture_shutdown, NULL,

		shutdown_task = kthread_create(rcu_torture_shutdown, NULL,

					       "rcu_torture_shutdown");

					       "rcu_torture_shutdown");

		if (IS_ERR(shutdown_task)) {

		if (IS_ERR(shutdown_task)) {

			firsterr = PTR_ERR(shutdown_task);

			firsterr = PTR_ERR(shutdown_task);
@@ -2159,6 +2160,7 @@ rcu_torture_init(void) 
			shutdown_task = NULL;

			shutdown_task = NULL;

			goto unwind;

			goto unwind;

		}

		}

		wake_up_process(shutdown_task);

	}

	}

	i = rcu_torture_onoff_init();

	i = rcu_torture_onoff_init();

	if (i != 0) {

	if (i != 0) {