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Commit 29fd9309 authored by Paul E. McKenney's avatar Paul E. McKenney
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rcu: Use funnel locking for synchronize_rcu_expedited()'s polling loop 



This commit gets rid of synchronize_rcu_expedited()'s mutex_trylock()
polling loop in favor of the funnel-locking scheme that was abstracted
from synchronize_sched_expedited().

Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
parent 7fd0ddc5

kernel/rcu/tree.c

+8 −7
Original line number Diff line number Diff line
@@ -3309,8 +3309,8 @@ static bool rcu_exp_gp_seq_done(struct rcu_state *rsp, unsigned long s) 
	return rcu_seq_done(&rsp->expedited_sequence, s);

}



/* Common code for synchronize_sched_expedited() work-done checking. */

static bool sync_sched_exp_wd(struct rcu_state *rsp, struct rcu_node *rnp,

/* Common code for synchronize_{rcu,sched}_expedited() work-done checking. */

static bool sync_exp_work_done(struct rcu_state *rsp, struct rcu_node *rnp,

			       atomic_long_t *stat, unsigned long s)

{

	if (rcu_exp_gp_seq_done(rsp, s)) {
@@ -3319,7 +3319,6 @@ static bool sync_sched_exp_wd(struct rcu_state *rsp, struct rcu_node *rnp, 
		/* Ensure test happens before caller kfree(). */

		smp_mb__before_atomic(); /* ^^^ */

		atomic_long_inc(stat);

		put_online_cpus();

		return true;

	}

	return false;
@@ -3345,14 +3344,14 @@ static struct rcu_node *exp_funnel_lock(struct rcu_state *rsp, unsigned long s) 
	 */

	rnp0 = per_cpu_ptr(rsp->rda, raw_smp_processor_id())->mynode;

	for (; rnp0 != NULL; rnp0 = rnp0->parent) {

		if (sync_sched_exp_wd(rsp, rnp1, &rsp->expedited_workdone1, s))

		if (sync_exp_work_done(rsp, rnp1, &rsp->expedited_workdone1, s))

			return NULL;

		mutex_lock(&rnp0->exp_funnel_mutex);

		if (rnp1)

			mutex_unlock(&rnp1->exp_funnel_mutex);

		rnp1 = rnp0;

	}

	if (sync_sched_exp_wd(rsp, rnp1, &rsp->expedited_workdone2, s))

	if (sync_exp_work_done(rsp, rnp1, &rsp->expedited_workdone2, s))

		return NULL;

	return rnp1;

}
@@ -3402,8 +3401,10 @@ void synchronize_sched_expedited(void) 
	WARN_ON_ONCE(cpu_is_offline(raw_smp_processor_id()));



	rnp = exp_funnel_lock(rsp, s);

	if (rnp == NULL)

	if (rnp == NULL) {

		put_online_cpus();

		return;  /* Someone else did our work for us. */

	}



	rcu_exp_gp_seq_start(rsp);

kernel/rcu/tree_plugin.h

+10 −26
Original line number Diff line number Diff line
@@ -536,7 +536,6 @@ void synchronize_rcu(void) 
EXPORT_SYMBOL_GPL(synchronize_rcu);



static DECLARE_WAIT_QUEUE_HEAD(sync_rcu_preempt_exp_wq);

static DEFINE_MUTEX(sync_rcu_preempt_exp_mutex);



/*

 * Return non-zero if there are any tasks in RCU read-side critical
@@ -556,7 +555,7 @@ static int rcu_preempted_readers_exp(struct rcu_node *rnp) 
 * for the current expedited grace period.  Works only for preemptible

 * RCU -- other RCU implementation use other means.

 *

 * Caller must hold sync_rcu_preempt_exp_mutex.

 * Caller must hold the root rcu_node's exp_funnel_mutex.

 */

static int sync_rcu_preempt_exp_done(struct rcu_node *rnp)

{
@@ -572,7 +571,7 @@ static int sync_rcu_preempt_exp_done(struct rcu_node *rnp) 
 * recursively up the tree.  (Calm down, calm down, we do the recursion

 * iteratively!)

 *

 * Caller must hold sync_rcu_preempt_exp_mutex.

 * Caller must hold the root rcu_node's exp_funnel_mutex.

 */

static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp,

			       bool wake)
@@ -611,7 +610,7 @@ static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp, 
 * set the ->expmask bits on the leaf rcu_node structures to tell phase 2

 * that work is needed here.

 *

 * Caller must hold sync_rcu_preempt_exp_mutex.

 * Caller must hold the root rcu_node's exp_funnel_mutex.

 */

static void

sync_rcu_preempt_exp_init1(struct rcu_state *rsp, struct rcu_node *rnp)
@@ -654,7 +653,7 @@ sync_rcu_preempt_exp_init1(struct rcu_state *rsp, struct rcu_node *rnp) 
 * invoke rcu_report_exp_rnp() to clear out the upper-level ->expmask bits,

 * enabling rcu_read_unlock_special() to do the bit-clearing.

 *

 * Caller must hold sync_rcu_preempt_exp_mutex.

 * Caller must hold the root rcu_node's exp_funnel_mutex.

 */

static void

sync_rcu_preempt_exp_init2(struct rcu_state *rsp, struct rcu_node *rnp)
@@ -702,29 +701,16 @@ sync_rcu_preempt_exp_init2(struct rcu_state *rsp, struct rcu_node *rnp) 
void synchronize_rcu_expedited(void)

{

	struct rcu_node *rnp;

	struct rcu_node *rnp_unlock;

	struct rcu_state *rsp = rcu_state_p;

	unsigned long s;

	int trycount = 0;



	s = rcu_exp_gp_seq_snap(rsp);



	/*

	 * Acquire lock, falling back to synchronize_rcu() if too many

	 * lock-acquisition failures.  Of course, if someone does the

	 * expedited grace period for us, just leave.

	 */

	while (!mutex_trylock(&sync_rcu_preempt_exp_mutex)) {

		if (rcu_exp_gp_seq_done(rsp, s))

			goto mb_ret; /* Others did our work for us. */

		if (trycount++ < 10) {

			udelay(trycount * num_online_cpus());

		} else {

			wait_rcu_gp(call_rcu);

			return;

		}

	}

	if (rcu_exp_gp_seq_done(rsp, s))

		goto unlock_mb_ret; /* Others did our work for us. */

	rnp_unlock = exp_funnel_lock(rsp, s);

	if (rnp_unlock == NULL)

		return;  /* Someone else did our work for us. */



	rcu_exp_gp_seq_start(rsp);



	/* force all RCU readers onto ->blkd_tasks lists. */
@@ -748,9 +734,7 @@ void synchronize_rcu_expedited(void) 


	/* Clean up and exit. */

	rcu_exp_gp_seq_end(rsp);

unlock_mb_ret:

	mutex_unlock(&sync_rcu_preempt_exp_mutex);

mb_ret:

	mutex_unlock(&rnp_unlock->exp_funnel_mutex);

	smp_mb(); /* ensure subsequent action seen after grace period. */

}

EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);