Merge "osq_lock: avoid live-lock issue for RT task"

#include <linux/percpu.h>

#include <linux/sched.h>

#include <linux/osq_lock.h>

#include <linux/sched/rt.h>

/*

 * An MCS like lock especially tailored for optimistic spinning for sleeping

{

	struct optimistic_spin_node *node = this_cpu_ptr(&osq_node);

	struct optimistic_spin_node *prev, *next;

	struct task_struct *task = current;

	int curr = encode_cpu(smp_processor_id());

	int old;

	while (!READ_ONCE(node->locked)) {

		/*

		 * If we need to reschedule bail... so we can block.

		 * If a task spins on owner on a CPU after acquiring

		 * osq_lock while a RT task spins on another CPU  to

		 * acquire osq_lock, it will starve the owner from

		 * completing if owner is to be scheduled on the same CPU.

		 * It will be a live lock.

		 */

		if (need_resched())

		if (need_resched() || rt_task(task))

			goto unqueue;

		cpu_relax_lowlatency();