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Commit a3883df3 authored by Paul E. McKenney's avatar Paul E. McKenney
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srcu: Use rnp->lock wrappers to replace explicit memory barriers 



This commit uses TREE RCU's rnp->lock wrappers to replace a few explicit
memory barriers.  This change also has the advantage of making SRCU's
memory-ordering properties be implemented in roughly the same way as they
are in Tree RCU.

Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
parent 83d40bd3

include/linux/srcutree.h

+4 −4
Original line number Diff line number Diff line
@@ -40,7 +40,7 @@ struct srcu_data { 
	unsigned long srcu_unlock_count[2];	/* Unlocks per CPU. */



	/* Update-side state. */

	spinlock_t lock ____cacheline_internodealigned_in_smp;

	raw_spinlock_t __private lock ____cacheline_internodealigned_in_smp;

	struct rcu_segcblist srcu_cblist;	/* List of callbacks.*/

	unsigned long srcu_gp_seq_needed;	/* Furthest future GP needed. */

	unsigned long srcu_gp_seq_needed_exp;	/* Furthest future exp GP. */
@@ -58,7 +58,7 @@ struct srcu_data { 
 * Node in SRCU combining tree, similar in function to rcu_data.

 */

struct srcu_node {

	spinlock_t lock;

	raw_spinlock_t __private lock;

	unsigned long srcu_have_cbs[4];		/* GP seq for children */

						/*  having CBs, but only */

						/*  is > ->srcu_gq_seq. */
@@ -78,7 +78,7 @@ struct srcu_struct { 
	struct srcu_node *level[RCU_NUM_LVLS + 1];

						/* First node at each level. */

	struct mutex srcu_cb_mutex;		/* Serialize CB preparation. */

	spinlock_t gp_lock;			/* protect ->srcu_cblist */

	raw_spinlock_t __private lock;		/* Protect counters */

	struct mutex srcu_gp_mutex;		/* Serialize GP work. */

	unsigned int srcu_idx;			/* Current rdr array element. */

	unsigned long srcu_gp_seq;		/* Grace-period seq #. */
@@ -109,7 +109,7 @@ void process_srcu(struct work_struct *work); 
#define __SRCU_STRUCT_INIT(name)					\

	{								\

		.sda = &name##_srcu_data,				\

		.gp_lock = __SPIN_LOCK_UNLOCKED(name.gp_lock),		\

		.lock = __RAW_SPIN_LOCK_UNLOCKED(name.lock),		\

		.srcu_gp_seq_needed = 0 - 1,				\

		__SRCU_DEP_MAP_INIT(name)				\

	}

kernel/rcu/srcutree.c

+43 −48
Original line number Diff line number Diff line
@@ -76,7 +76,7 @@ static void init_srcu_struct_nodes(struct srcu_struct *sp, bool is_static) 


	/* Each pass through this loop initializes one srcu_node structure. */

	rcu_for_each_node_breadth_first(sp, snp) {

		spin_lock_init(&snp->lock);

		raw_spin_lock_init(&ACCESS_PRIVATE(snp, lock));

		WARN_ON_ONCE(ARRAY_SIZE(snp->srcu_have_cbs) !=

			     ARRAY_SIZE(snp->srcu_data_have_cbs));

		for (i = 0; i < ARRAY_SIZE(snp->srcu_have_cbs); i++) {
@@ -110,7 +110,7 @@ static void init_srcu_struct_nodes(struct srcu_struct *sp, bool is_static) 
	snp_first = sp->level[level];

	for_each_possible_cpu(cpu) {

		sdp = per_cpu_ptr(sp->sda, cpu);

		spin_lock_init(&sdp->lock);

		raw_spin_lock_init(&ACCESS_PRIVATE(sdp, lock));

		rcu_segcblist_init(&sdp->srcu_cblist);

		sdp->srcu_cblist_invoking = false;

		sdp->srcu_gp_seq_needed = sp->srcu_gp_seq;
@@ -169,7 +169,7 @@ int __init_srcu_struct(struct srcu_struct *sp, const char *name, 
	/* Don't re-initialize a lock while it is held. */

	debug_check_no_locks_freed((void *)sp, sizeof(*sp));

	lockdep_init_map(&sp->dep_map, name, key, 0);

	spin_lock_init(&sp->gp_lock);

	raw_spin_lock_init(&ACCESS_PRIVATE(sp, lock));

	return init_srcu_struct_fields(sp, false);

}

EXPORT_SYMBOL_GPL(__init_srcu_struct);
@@ -186,7 +186,7 @@ EXPORT_SYMBOL_GPL(__init_srcu_struct); 
 */

int init_srcu_struct(struct srcu_struct *sp)

{

	spin_lock_init(&sp->gp_lock);

	raw_spin_lock_init(&ACCESS_PRIVATE(sp, lock));

	return init_srcu_struct_fields(sp, false);

}

EXPORT_SYMBOL_GPL(init_srcu_struct);
@@ -197,7 +197,7 @@ EXPORT_SYMBOL_GPL(init_srcu_struct); 
 * First-use initialization of statically allocated srcu_struct

 * structure.  Wiring up the combining tree is more than can be

 * done with compile-time initialization, so this check is added

 * to each update-side SRCU primitive.  Use ->gp_lock, which -is-

 * to each update-side SRCU primitive.  Use sp->lock, which -is-

 * compile-time initialized, to resolve races involving multiple

 * CPUs trying to garner first-use privileges.

 */
@@ -209,13 +209,13 @@ static void check_init_srcu_struct(struct srcu_struct *sp) 
	/* The smp_load_acquire() pairs with the smp_store_release(). */

	if (!rcu_seq_state(smp_load_acquire(&sp->srcu_gp_seq_needed))) /*^^^*/

		return; /* Already initialized. */

	spin_lock_irqsave(&sp->gp_lock, flags);

	raw_spin_lock_irqsave_rcu_node(sp, flags);

	if (!rcu_seq_state(sp->srcu_gp_seq_needed)) {

		spin_unlock_irqrestore(&sp->gp_lock, flags);

		raw_spin_unlock_irqrestore_rcu_node(sp, flags);

		return;

	}

	init_srcu_struct_fields(sp, true);

	spin_unlock_irqrestore(&sp->gp_lock, flags);

	raw_spin_unlock_irqrestore_rcu_node(sp, flags);

}



/*
@@ -411,8 +411,7 @@ static void srcu_gp_start(struct srcu_struct *sp) 
	struct srcu_data *sdp = this_cpu_ptr(sp->sda);

	int state;



	RCU_LOCKDEP_WARN(!lockdep_is_held(&sp->gp_lock),

			 "Invoked srcu_gp_start() without ->gp_lock!");

	lockdep_assert_held(&sp->lock);

	WARN_ON_ONCE(ULONG_CMP_GE(sp->srcu_gp_seq, sp->srcu_gp_seq_needed));

	rcu_segcblist_advance(&sdp->srcu_cblist,

			      rcu_seq_current(&sp->srcu_gp_seq));
@@ -513,7 +512,7 @@ static void srcu_gp_end(struct srcu_struct *sp) 
	mutex_lock(&sp->srcu_cb_mutex);



	/* End the current grace period. */

	spin_lock_irq(&sp->gp_lock);

	raw_spin_lock_irq_rcu_node(sp);

	idx = rcu_seq_state(sp->srcu_gp_seq);

	WARN_ON_ONCE(idx != SRCU_STATE_SCAN2);

	cbdelay = srcu_get_delay(sp);
@@ -522,7 +521,7 @@ static void srcu_gp_end(struct srcu_struct *sp) 
	gpseq = rcu_seq_current(&sp->srcu_gp_seq);

	if (ULONG_CMP_LT(sp->srcu_gp_seq_needed_exp, gpseq))

		sp->srcu_gp_seq_needed_exp = gpseq;

	spin_unlock_irq(&sp->gp_lock);

	raw_spin_unlock_irq_rcu_node(sp);

	mutex_unlock(&sp->srcu_gp_mutex);

	/* A new grace period can start at this point.  But only one. */
@@ -530,7 +529,7 @@ static void srcu_gp_end(struct srcu_struct *sp) 
	idx = rcu_seq_ctr(gpseq) % ARRAY_SIZE(snp->srcu_have_cbs);

	idxnext = (idx + 1) % ARRAY_SIZE(snp->srcu_have_cbs);

	rcu_for_each_node_breadth_first(sp, snp) {

		spin_lock_irq(&snp->lock);

		raw_spin_lock_irq_rcu_node(snp);

		cbs = false;

		if (snp >= sp->level[rcu_num_lvls - 1])

			cbs = snp->srcu_have_cbs[idx] == gpseq;
@@ -540,21 +539,19 @@ static void srcu_gp_end(struct srcu_struct *sp) 
			snp->srcu_gp_seq_needed_exp = gpseq;

		mask = snp->srcu_data_have_cbs[idx];

		snp->srcu_data_have_cbs[idx] = 0;

		spin_unlock_irq(&snp->lock);

		if (cbs) {

			smp_mb(); /* GP end before CB invocation. */

		raw_spin_unlock_irq_rcu_node(snp);

		if (cbs)

			srcu_schedule_cbs_snp(sp, snp, mask, cbdelay);

		}



		/* Occasionally prevent srcu_data counter wrap. */

		if (!(gpseq & counter_wrap_check))

			for (cpu = snp->grplo; cpu <= snp->grphi; cpu++) {

				sdp = per_cpu_ptr(sp->sda, cpu);

				spin_lock_irqsave(&sdp->lock, flags);

				raw_spin_lock_irqsave_rcu_node(sdp, flags);

				if (ULONG_CMP_GE(gpseq,

						 sdp->srcu_gp_seq_needed + 100))

					sdp->srcu_gp_seq_needed = gpseq;

				spin_unlock_irqrestore(&sdp->lock, flags);

				raw_spin_unlock_irqrestore_rcu_node(sdp, flags);

			}

	}
@@ -562,17 +559,17 @@ static void srcu_gp_end(struct srcu_struct *sp) 
	mutex_unlock(&sp->srcu_cb_mutex);



	/* Start a new grace period if needed. */

	spin_lock_irq(&sp->gp_lock);

	raw_spin_lock_irq_rcu_node(sp);

	gpseq = rcu_seq_current(&sp->srcu_gp_seq);

	if (!rcu_seq_state(gpseq) &&

	    ULONG_CMP_LT(gpseq, sp->srcu_gp_seq_needed)) {

		srcu_gp_start(sp);

		spin_unlock_irq(&sp->gp_lock);

		raw_spin_unlock_irq_rcu_node(sp);

		/* Throttle expedited grace periods: Should be rare! */

		srcu_reschedule(sp, rcu_seq_ctr(gpseq) & 0x3ff

				    ? 0 : SRCU_INTERVAL);

	} else {

		spin_unlock_irq(&sp->gp_lock);

		raw_spin_unlock_irq_rcu_node(sp);

	}

}
@@ -592,18 +589,18 @@ static void srcu_funnel_exp_start(struct srcu_struct *sp, struct srcu_node *snp, 
		if (rcu_seq_done(&sp->srcu_gp_seq, s) ||

		    ULONG_CMP_GE(READ_ONCE(snp->srcu_gp_seq_needed_exp), s))

			return;

		spin_lock_irqsave(&snp->lock, flags);

		raw_spin_lock_irqsave_rcu_node(snp, flags);

		if (ULONG_CMP_GE(snp->srcu_gp_seq_needed_exp, s)) {

			spin_unlock_irqrestore(&snp->lock, flags);

			raw_spin_unlock_irqrestore_rcu_node(snp, flags);

			return;

		}

		WRITE_ONCE(snp->srcu_gp_seq_needed_exp, s);

		spin_unlock_irqrestore(&snp->lock, flags);

		raw_spin_unlock_irqrestore_rcu_node(snp, flags);

	}

	spin_lock_irqsave(&sp->gp_lock, flags);

	raw_spin_lock_irqsave_rcu_node(sp, flags);

	if (!ULONG_CMP_LT(sp->srcu_gp_seq_needed_exp, s))

		sp->srcu_gp_seq_needed_exp = s;

	spin_unlock_irqrestore(&sp->gp_lock, flags);

	raw_spin_unlock_irqrestore_rcu_node(sp, flags);

}



/*
@@ -625,14 +622,13 @@ static void srcu_funnel_gp_start(struct srcu_struct *sp, struct srcu_data *sdp, 
	for (; snp != NULL; snp = snp->srcu_parent) {

		if (rcu_seq_done(&sp->srcu_gp_seq, s) && snp != sdp->mynode)

			return; /* GP already done and CBs recorded. */

		spin_lock_irqsave(&snp->lock, flags);

		raw_spin_lock_irqsave_rcu_node(snp, flags);

		if (ULONG_CMP_GE(snp->srcu_have_cbs[idx], s)) {

			snp_seq = snp->srcu_have_cbs[idx];

			if (snp == sdp->mynode && snp_seq == s)

				snp->srcu_data_have_cbs[idx] |= sdp->grpmask;

			spin_unlock_irqrestore(&snp->lock, flags);

			raw_spin_unlock_irqrestore_rcu_node(snp, flags);

			if (snp == sdp->mynode && snp_seq != s) {

				smp_mb(); /* CBs after GP! */

				srcu_schedule_cbs_sdp(sdp, do_norm

							   ? SRCU_INTERVAL

							   : 0);
@@ -647,11 +643,11 @@ static void srcu_funnel_gp_start(struct srcu_struct *sp, struct srcu_data *sdp, 
			snp->srcu_data_have_cbs[idx] |= sdp->grpmask;

		if (!do_norm && ULONG_CMP_LT(snp->srcu_gp_seq_needed_exp, s))

			snp->srcu_gp_seq_needed_exp = s;

		spin_unlock_irqrestore(&snp->lock, flags);

		raw_spin_unlock_irqrestore_rcu_node(snp, flags);

	}



	/* Top of tree, must ensure the grace period will be started. */

	spin_lock_irqsave(&sp->gp_lock, flags);

	raw_spin_lock_irqsave_rcu_node(sp, flags);

	if (ULONG_CMP_LT(sp->srcu_gp_seq_needed, s)) {

		/*

		 * Record need for grace period s.  Pair with load
@@ -670,7 +666,7 @@ static void srcu_funnel_gp_start(struct srcu_struct *sp, struct srcu_data *sdp, 
		queue_delayed_work(system_power_efficient_wq, &sp->work,

				   srcu_get_delay(sp));

	}

	spin_unlock_irqrestore(&sp->gp_lock, flags);

	raw_spin_unlock_irqrestore_rcu_node(sp, flags);

}



/*
@@ -833,7 +829,7 @@ void __call_srcu(struct srcu_struct *sp, struct rcu_head *rhp, 
	rhp->func = func;

	local_irq_save(flags);

	sdp = this_cpu_ptr(sp->sda);

	spin_lock(&sdp->lock);

	raw_spin_lock_rcu_node(sdp);

	rcu_segcblist_enqueue(&sdp->srcu_cblist, rhp, false);

	rcu_segcblist_advance(&sdp->srcu_cblist,

			      rcu_seq_current(&sp->srcu_gp_seq));
@@ -847,7 +843,7 @@ void __call_srcu(struct srcu_struct *sp, struct rcu_head *rhp, 
		sdp->srcu_gp_seq_needed_exp = s;

		needexp = true;

	}

	spin_unlock_irqrestore(&sdp->lock, flags);

	raw_spin_unlock_irqrestore_rcu_node(sdp, flags);

	if (needgp)

		srcu_funnel_gp_start(sp, sdp, s, do_norm);

	else if (needexp)
@@ -1018,7 +1014,7 @@ void srcu_barrier(struct srcu_struct *sp) 
	 */

	for_each_possible_cpu(cpu) {

		sdp = per_cpu_ptr(sp->sda, cpu);

		spin_lock_irq(&sdp->lock);

		raw_spin_lock_irq_rcu_node(sdp);

		atomic_inc(&sp->srcu_barrier_cpu_cnt);

		sdp->srcu_barrier_head.func = srcu_barrier_cb;

		debug_rcu_head_queue(&sdp->srcu_barrier_head);
@@ -1027,7 +1023,7 @@ void srcu_barrier(struct srcu_struct *sp) 
			debug_rcu_head_unqueue(&sdp->srcu_barrier_head);

			atomic_dec(&sp->srcu_barrier_cpu_cnt);

		}

		spin_unlock_irq(&sdp->lock);

		raw_spin_unlock_irq_rcu_node(sdp);

	}



	/* Remove the initial count, at which point reaching zero can happen. */
@@ -1076,17 +1072,17 @@ static void srcu_advance_state(struct srcu_struct *sp) 
	 */

	idx = rcu_seq_state(smp_load_acquire(&sp->srcu_gp_seq)); /* ^^^ */

	if (idx == SRCU_STATE_IDLE) {

		spin_lock_irq(&sp->gp_lock);

		raw_spin_lock_irq_rcu_node(sp);

		if (ULONG_CMP_GE(sp->srcu_gp_seq, sp->srcu_gp_seq_needed)) {

			WARN_ON_ONCE(rcu_seq_state(sp->srcu_gp_seq));

			spin_unlock_irq(&sp->gp_lock);

			raw_spin_unlock_irq_rcu_node(sp);

			mutex_unlock(&sp->srcu_gp_mutex);

			return;

		}

		idx = rcu_seq_state(READ_ONCE(sp->srcu_gp_seq));

		if (idx == SRCU_STATE_IDLE)

			srcu_gp_start(sp);

		spin_unlock_irq(&sp->gp_lock);

		raw_spin_unlock_irq_rcu_node(sp);

		if (idx != SRCU_STATE_IDLE) {

			mutex_unlock(&sp->srcu_gp_mutex);

			return; /* Someone else started the grace period. */
@@ -1135,20 +1131,19 @@ static void srcu_invoke_callbacks(struct work_struct *work) 
	sdp = container_of(work, struct srcu_data, work.work);

	sp = sdp->sp;

	rcu_cblist_init(&ready_cbs);

	spin_lock_irq(&sdp->lock);

	smp_mb(); /* Old grace periods before callback invocation! */

	raw_spin_lock_irq_rcu_node(sdp);

	rcu_segcblist_advance(&sdp->srcu_cblist,

			      rcu_seq_current(&sp->srcu_gp_seq));

	if (sdp->srcu_cblist_invoking ||

	    !rcu_segcblist_ready_cbs(&sdp->srcu_cblist)) {

		spin_unlock_irq(&sdp->lock);

		raw_spin_unlock_irq_rcu_node(sdp);

		return;  /* Someone else on the job or nothing to do. */

	}



	/* We are on the job!  Extract and invoke ready callbacks. */

	sdp->srcu_cblist_invoking = true;

	rcu_segcblist_extract_done_cbs(&sdp->srcu_cblist, &ready_cbs);

	spin_unlock_irq(&sdp->lock);

	raw_spin_unlock_irq_rcu_node(sdp);

	rhp = rcu_cblist_dequeue(&ready_cbs);

	for (; rhp != NULL; rhp = rcu_cblist_dequeue(&ready_cbs)) {

		debug_rcu_head_unqueue(rhp);
@@ -1161,13 +1156,13 @@ static void srcu_invoke_callbacks(struct work_struct *work) 
	 * Update counts, accelerate new callbacks, and if needed,

	 * schedule another round of callback invocation.

	 */

	spin_lock_irq(&sdp->lock);

	raw_spin_lock_irq_rcu_node(sdp);

	rcu_segcblist_insert_count(&sdp->srcu_cblist, &ready_cbs);

	(void)rcu_segcblist_accelerate(&sdp->srcu_cblist,

				       rcu_seq_snap(&sp->srcu_gp_seq));

	sdp->srcu_cblist_invoking = false;

	more = rcu_segcblist_ready_cbs(&sdp->srcu_cblist);

	spin_unlock_irq(&sdp->lock);

	raw_spin_unlock_irq_rcu_node(sdp);

	if (more)

		srcu_schedule_cbs_sdp(sdp, 0);

}
@@ -1180,7 +1175,7 @@ static void srcu_reschedule(struct srcu_struct *sp, unsigned long delay) 
{

	bool pushgp = true;



	spin_lock_irq(&sp->gp_lock);

	raw_spin_lock_irq_rcu_node(sp);

	if (ULONG_CMP_GE(sp->srcu_gp_seq, sp->srcu_gp_seq_needed)) {

		if (!WARN_ON_ONCE(rcu_seq_state(sp->srcu_gp_seq))) {

			/* All requests fulfilled, time to go idle. */
@@ -1190,7 +1185,7 @@ static void srcu_reschedule(struct srcu_struct *sp, unsigned long delay) 
		/* Outstanding request and no GP.  Start one. */

		srcu_gp_start(sp);

	}

	spin_unlock_irq(&sp->gp_lock);

	raw_spin_unlock_irq_rcu_node(sp);



	if (pushgp)

		queue_delayed_work(system_power_efficient_wq, &sp->work, delay);