locktorture: Dump CPUs running writer tasks when RCU stalls

This commit force stack dumps of the CPUs running writer tasks when
an RCU CPU stall warning occurs.  This is helpful in the common case
where RCU isn't being stalled by all of those tasks, and thus won't dump
their stacks.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

Author: paulmckrcu

kernel/locking/locktorture.c

@@ -284,6 +284,7 @@ void __weak spinlock_dump(spinlock_t *sp, bool full)
 
 static int torture_spin_lock_dump(struct notifier_block *nb, unsigned long v, void *ptr)
 {
+	int cpu;
 	struct task_struct *t = READ_ONCE(lock_is_write_held);
 
 	pr_alert("%s invoked: v=%lu, duration=%lu.\n", __func__, v, (unsigned long)ptr);
@@ -295,6 +296,8 @@ static int torture_spin_lock_dump(struct notifier_block *nb, unsigned long v, vo
 		sched_show_task(t);
 	}
 	spinlock_dump(&torture_spinlock, true);
+	for_each_cpu(cpu, bind_writers)
+		dump_cpu_task(cpu);
 	return NOTIFY_OK;
 }