Commit 1aa03f11 authored by Paul E. McKenney's avatar Paul E. McKenney Committed by Paul E. McKenney
Browse files

rcu: Simplify unboosting checks 



This is a port of commit #82e78d80 from TREE_PREEMPT_RCU to
TINY_PREEMPT_RCU.

This commit uses the fact that current->rcu_boost_mutex is set
any time that the RCU_READ_UNLOCK_BOOSTED flag is set in the
current->rcu_read_unlock_special bitmask.  This allows tests of
the bit to be changed to tests of the pointer, which in turn allows
the RCU_READ_UNLOCK_BOOSTED flag to be eliminated.

Please note that the check of current->rcu_read_unlock_special need not
change because any time that RCU_READ_UNLOCK_BOOSTED was set, so was
RCU_READ_UNLOCK_BLOCKED.  Therefore, __rcu_read_unlock() can continue
testing current->rcu_read_unlock_special for non-zero, as before.

Signed-off-by: default avatarPaul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
parent 8762705a

include/linux/sched.h

+1 −2
Original line number Diff line number Diff line
@@ -1864,8 +1864,7 @@ extern void task_clear_jobctl_pending(struct task_struct *task, 
#ifdef CONFIG_PREEMPT_RCU



#define RCU_READ_UNLOCK_BLOCKED (1 << 0) /* blocked while in RCU read-side. */

#define RCU_READ_UNLOCK_BOOSTED (1 << 1) /* boosted while in RCU read-side. */

#define RCU_READ_UNLOCK_NEED_QS (1 << 2) /* RCU core needs CPU response. */

#define RCU_READ_UNLOCK_NEED_QS (1 << 1) /* RCU core needs CPU response. */



static inline void rcu_copy_process(struct task_struct *p)

{

kernel/rcutiny_plugin.h

+6 −4
Original line number Diff line number Diff line
@@ -318,7 +318,6 @@ static int rcu_boost(void) 
	t = container_of(tb, struct task_struct, rcu_node_entry);

	rt_mutex_init_proxy_locked(&mtx, t);

	t->rcu_boost_mutex = &mtx;

	t->rcu_read_unlock_special |= RCU_READ_UNLOCK_BOOSTED;

	raw_local_irq_restore(flags);

	rt_mutex_lock(&mtx);

	rt_mutex_unlock(&mtx);  /* Keep lockdep happy. */
@@ -550,6 +549,9 @@ static noinline void rcu_read_unlock_special(struct task_struct *t) 
	int empty_exp;

	unsigned long flags;

	struct list_head *np;

#ifdef CONFIG_RCU_BOOST

	struct rt_mutex *rbmp = NULL;

#endif /* #ifdef CONFIG_RCU_BOOST */

	int special;



	/*
@@ -615,10 +617,10 @@ static noinline void rcu_read_unlock_special(struct task_struct *t) 
	}

#ifdef CONFIG_RCU_BOOST

	/* Unboost self if was boosted. */

	if (special & RCU_READ_UNLOCK_BOOSTED) {

		t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_BOOSTED;

		rt_mutex_unlock(t->rcu_boost_mutex);

	if (t->rcu_boost_mutex != NULL) {

		rbmp = t->rcu_boost_mutex;

		t->rcu_boost_mutex = NULL;

		rt_mutex_unlock(rbmp);

	}

#endif /* #ifdef CONFIG_RCU_BOOST */

	local_irq_restore(flags);

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