rcu: Fix bug in rcu_barrier() torture test
The child threads in the rcu_torture_barrier_cbs() are improperly synchronized, which can cause the rcu_barrier() tests to hang. The failure mode is as follows: 1. CPU 0 running in rcu_torture_barrier() sets barrier_cbs_count to n_barrier_cbs. 2. CPU 1 running in rcu_torture_barrier_cbs() wakes up, posts its RCU callback, and atomically decrements barrier_cbs_count. Because barrier_cbs_count is not zero, it does not do the wake_up(). 3. CPU 2 running in rcu_torture_barrier_cbs() wakes up, but finds that barrier_cbs_count is not equal to n_barrier_cbs, and so returns to sleep. 4. The value of barrier_cbs_count therefore never reaches zero, which causes the test to hang. This commit therefore uses a phase variable to coordinate the test, preventing this scenario from occurring. Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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@ -206,6 +206,7 @@ static unsigned long boost_starttime; /* jiffies of next boost test start. */
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DEFINE_MUTEX(boost_mutex); /* protect setting boost_starttime */
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DEFINE_MUTEX(boost_mutex); /* protect setting boost_starttime */
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/* and boost task create/destroy. */
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/* and boost task create/destroy. */
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static atomic_t barrier_cbs_count; /* Barrier callbacks registered. */
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static atomic_t barrier_cbs_count; /* Barrier callbacks registered. */
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static bool barrier_phase; /* Test phase. */
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static atomic_t barrier_cbs_invoked; /* Barrier callbacks invoked. */
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static atomic_t barrier_cbs_invoked; /* Barrier callbacks invoked. */
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static wait_queue_head_t *barrier_cbs_wq; /* Coordinate barrier testing. */
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static wait_queue_head_t *barrier_cbs_wq; /* Coordinate barrier testing. */
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static DECLARE_WAIT_QUEUE_HEAD(barrier_wq);
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static DECLARE_WAIT_QUEUE_HEAD(barrier_wq);
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@ -1642,6 +1643,7 @@ void rcu_torture_barrier_cbf(struct rcu_head *rcu)
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static int rcu_torture_barrier_cbs(void *arg)
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static int rcu_torture_barrier_cbs(void *arg)
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{
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{
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long myid = (long)arg;
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long myid = (long)arg;
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bool lastphase = 0;
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struct rcu_head rcu;
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struct rcu_head rcu;
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init_rcu_head_on_stack(&rcu);
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init_rcu_head_on_stack(&rcu);
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@ -1649,9 +1651,11 @@ static int rcu_torture_barrier_cbs(void *arg)
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set_user_nice(current, 19);
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set_user_nice(current, 19);
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do {
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do {
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wait_event(barrier_cbs_wq[myid],
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wait_event(barrier_cbs_wq[myid],
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atomic_read(&barrier_cbs_count) == n_barrier_cbs ||
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barrier_phase != lastphase ||
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kthread_should_stop() ||
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kthread_should_stop() ||
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fullstop != FULLSTOP_DONTSTOP);
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fullstop != FULLSTOP_DONTSTOP);
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lastphase = barrier_phase;
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smp_mb(); /* ensure barrier_phase load before ->call(). */
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if (kthread_should_stop() || fullstop != FULLSTOP_DONTSTOP)
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if (kthread_should_stop() || fullstop != FULLSTOP_DONTSTOP)
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break;
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break;
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cur_ops->call(&rcu, rcu_torture_barrier_cbf);
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cur_ops->call(&rcu, rcu_torture_barrier_cbf);
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@ -1676,7 +1680,8 @@ static int rcu_torture_barrier(void *arg)
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do {
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do {
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atomic_set(&barrier_cbs_invoked, 0);
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atomic_set(&barrier_cbs_invoked, 0);
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atomic_set(&barrier_cbs_count, n_barrier_cbs);
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atomic_set(&barrier_cbs_count, n_barrier_cbs);
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/* wake_up() path contains the required barriers. */
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smp_mb(); /* Ensure barrier_phase after prior assignments. */
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barrier_phase = !barrier_phase;
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for (i = 0; i < n_barrier_cbs; i++)
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for (i = 0; i < n_barrier_cbs; i++)
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wake_up(&barrier_cbs_wq[i]);
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wake_up(&barrier_cbs_wq[i]);
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wait_event(barrier_wq,
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wait_event(barrier_wq,
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