Commit 3549c2bc authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

rcu: Move expedited code from tree.c to tree_exp.h 



People have been having some difficulty finding their way around the
RCU code.  This commit therefore pulls some of the expedited grace-period
code from tree.c to a new tree_exp.h file.  This commit is strictly code
movement, with the exception of a forward declaration that was added
for the sync_sched_exp_online_cleanup() function.

A subsequent commit will move the remaining expedited grace-period code
from tree_plugin.h to tree_exp.h.

Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
parent d3acab65

kernel/rcu/tree.c

+2 −543
Original line number Diff line number Diff line
@@ -159,6 +159,7 @@ static void invoke_rcu_core(void); 
static void invoke_rcu_callbacks(struct rcu_state *rsp, struct rcu_data *rdp);

static void rcu_report_exp_rdp(struct rcu_state *rsp,

			       struct rcu_data *rdp, bool wake);

static void sync_sched_exp_online_cleanup(int cpu);



/* rcuc/rcub kthread realtime priority */

#ifdef CONFIG_RCU_KTHREAD_PRIO
@@ -3447,549 +3448,6 @@ static bool rcu_seq_done(unsigned long *sp, unsigned long s) 
	return ULONG_CMP_GE(READ_ONCE(*sp), s);

}



/* Wrapper functions for expedited grace periods.  */

static void rcu_exp_gp_seq_start(struct rcu_state *rsp)

{

	rcu_seq_start(&rsp->expedited_sequence);

}

static void rcu_exp_gp_seq_end(struct rcu_state *rsp)

{

	rcu_seq_end(&rsp->expedited_sequence);

	smp_mb(); /* Ensure that consecutive grace periods serialize. */

}

static unsigned long rcu_exp_gp_seq_snap(struct rcu_state *rsp)

{

	unsigned long s;



	smp_mb(); /* Caller's modifications seen first by other CPUs. */

	s = rcu_seq_snap(&rsp->expedited_sequence);

	trace_rcu_exp_grace_period(rsp->name, s, TPS("snap"));

	return s;

}

static bool rcu_exp_gp_seq_done(struct rcu_state *rsp, unsigned long s)

{

	return rcu_seq_done(&rsp->expedited_sequence, s);

}



/*

 * Reset the ->expmaskinit values in the rcu_node tree to reflect any

 * recent CPU-online activity.  Note that these masks are not cleared

 * when CPUs go offline, so they reflect the union of all CPUs that have

 * ever been online.  This means that this function normally takes its

 * no-work-to-do fastpath.

 */

static void sync_exp_reset_tree_hotplug(struct rcu_state *rsp)

{

	bool done;

	unsigned long flags;

	unsigned long mask;

	unsigned long oldmask;

	int ncpus = READ_ONCE(rsp->ncpus);

	struct rcu_node *rnp;

	struct rcu_node *rnp_up;



	/* If no new CPUs onlined since last time, nothing to do. */

	if (likely(ncpus == rsp->ncpus_snap))

		return;

	rsp->ncpus_snap = ncpus;



	/*

	 * Each pass through the following loop propagates newly onlined

	 * CPUs for the current rcu_node structure up the rcu_node tree.

	 */

	rcu_for_each_leaf_node(rsp, rnp) {

		raw_spin_lock_irqsave_rcu_node(rnp, flags);

		if (rnp->expmaskinit == rnp->expmaskinitnext) {

			raw_spin_unlock_irqrestore_rcu_node(rnp, flags);

			continue;  /* No new CPUs, nothing to do. */

		}



		/* Update this node's mask, track old value for propagation. */

		oldmask = rnp->expmaskinit;

		rnp->expmaskinit = rnp->expmaskinitnext;

		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);



		/* If was already nonzero, nothing to propagate. */

		if (oldmask)

			continue;



		/* Propagate the new CPU up the tree. */

		mask = rnp->grpmask;

		rnp_up = rnp->parent;

		done = false;

		while (rnp_up) {

			raw_spin_lock_irqsave_rcu_node(rnp_up, flags);

			if (rnp_up->expmaskinit)

				done = true;

			rnp_up->expmaskinit |= mask;

			raw_spin_unlock_irqrestore_rcu_node(rnp_up, flags);

			if (done)

				break;

			mask = rnp_up->grpmask;

			rnp_up = rnp_up->parent;

		}

	}

}



/*

 * Reset the ->expmask values in the rcu_node tree in preparation for

 * a new expedited grace period.

 */

static void __maybe_unused sync_exp_reset_tree(struct rcu_state *rsp)

{

	unsigned long flags;

	struct rcu_node *rnp;



	sync_exp_reset_tree_hotplug(rsp);

	rcu_for_each_node_breadth_first(rsp, rnp) {

		raw_spin_lock_irqsave_rcu_node(rnp, flags);

		WARN_ON_ONCE(rnp->expmask);

		rnp->expmask = rnp->expmaskinit;

		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);

	}

}



/*

 * Return non-zero if there is no RCU expedited grace period in progress

 * for the specified rcu_node structure, in other words, if all CPUs and

 * tasks covered by the specified rcu_node structure have done their bit

 * for the current expedited grace period.  Works only for preemptible

 * RCU -- other RCU implementation use other means.

 *

 * Caller must hold the rcu_state's exp_mutex.

 */

static int sync_rcu_preempt_exp_done(struct rcu_node *rnp)

{

	return rnp->exp_tasks == NULL &&

	       READ_ONCE(rnp->expmask) == 0;

}



/*

 * Report the exit from RCU read-side critical section for the last task

 * that queued itself during or before the current expedited preemptible-RCU

 * grace period.  This event is reported either to the rcu_node structure on

 * which the task was queued or to one of that rcu_node structure's ancestors,

 * recursively up the tree.  (Calm down, calm down, we do the recursion

 * iteratively!)

 *

 * Caller must hold the rcu_state's exp_mutex and the specified rcu_node

 * structure's ->lock.

 */

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

				 bool wake, unsigned long flags)

	__releases(rnp->lock)

{

	unsigned long mask;



	for (;;) {

		if (!sync_rcu_preempt_exp_done(rnp)) {

			if (!rnp->expmask)

				rcu_initiate_boost(rnp, flags);

			else

				raw_spin_unlock_irqrestore_rcu_node(rnp, flags);

			break;

		}

		if (rnp->parent == NULL) {

			raw_spin_unlock_irqrestore_rcu_node(rnp, flags);

			if (wake) {

				smp_mb(); /* EGP done before wake_up(). */

				swake_up(&rsp->expedited_wq);

			}

			break;

		}

		mask = rnp->grpmask;

		raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled */

		rnp = rnp->parent;

		raw_spin_lock_rcu_node(rnp); /* irqs already disabled */

		WARN_ON_ONCE(!(rnp->expmask & mask));

		rnp->expmask &= ~mask;

	}

}



/*

 * Report expedited quiescent state for specified node.  This is a

 * lock-acquisition wrapper function for __rcu_report_exp_rnp().

 *

 * Caller must hold the rcu_state's exp_mutex.

 */

static void __maybe_unused rcu_report_exp_rnp(struct rcu_state *rsp,

					      struct rcu_node *rnp, bool wake)

{

	unsigned long flags;



	raw_spin_lock_irqsave_rcu_node(rnp, flags);

	__rcu_report_exp_rnp(rsp, rnp, wake, flags);

}



/*

 * Report expedited quiescent state for multiple CPUs, all covered by the

 * specified leaf rcu_node structure.  Caller must hold the rcu_state's

 * exp_mutex.

 */

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

				    unsigned long mask, bool wake)

{

	unsigned long flags;



	raw_spin_lock_irqsave_rcu_node(rnp, flags);

	if (!(rnp->expmask & mask)) {

		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);

		return;

	}

	rnp->expmask &= ~mask;

	__rcu_report_exp_rnp(rsp, rnp, wake, flags); /* Releases rnp->lock. */

}



/*

 * Report expedited quiescent state for specified rcu_data (CPU).

 */

static void rcu_report_exp_rdp(struct rcu_state *rsp, struct rcu_data *rdp,

			       bool wake)

{

	rcu_report_exp_cpu_mult(rsp, rdp->mynode, rdp->grpmask, wake);

}



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

static bool sync_exp_work_done(struct rcu_state *rsp, atomic_long_t *stat,

			       unsigned long s)

{

	if (rcu_exp_gp_seq_done(rsp, s)) {

		trace_rcu_exp_grace_period(rsp->name, s, TPS("done"));

		/* Ensure test happens before caller kfree(). */

		smp_mb__before_atomic(); /* ^^^ */

		atomic_long_inc(stat);

		return true;

	}

	return false;

}



/*

 * Funnel-lock acquisition for expedited grace periods.  Returns true

 * if some other task completed an expedited grace period that this task

 * can piggy-back on, and with no mutex held.  Otherwise, returns false

 * with the mutex held, indicating that the caller must actually do the

 * expedited grace period.

 */

static bool exp_funnel_lock(struct rcu_state *rsp, unsigned long s)

{

	struct rcu_data *rdp = per_cpu_ptr(rsp->rda, raw_smp_processor_id());

	struct rcu_node *rnp = rdp->mynode;

	struct rcu_node *rnp_root = rcu_get_root(rsp);



	/* Low-contention fastpath. */

	if (ULONG_CMP_LT(READ_ONCE(rnp->exp_seq_rq), s) &&

	    (rnp == rnp_root ||

	     ULONG_CMP_LT(READ_ONCE(rnp_root->exp_seq_rq), s)) &&

	    !mutex_is_locked(&rsp->exp_mutex) &&

	    mutex_trylock(&rsp->exp_mutex))

		goto fastpath;



	/*

	 * Each pass through the following loop works its way up

	 * the rcu_node tree, returning if others have done the work or

	 * otherwise falls through to acquire rsp->exp_mutex.  The mapping

	 * from CPU to rcu_node structure can be inexact, as it is just

	 * promoting locality and is not strictly needed for correctness.

	 */

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

		if (sync_exp_work_done(rsp, &rdp->exp_workdone1, s))

			return true;



		/* Work not done, either wait here or go up. */

		spin_lock(&rnp->exp_lock);

		if (ULONG_CMP_GE(rnp->exp_seq_rq, s)) {



			/* Someone else doing GP, so wait for them. */

			spin_unlock(&rnp->exp_lock);

			trace_rcu_exp_funnel_lock(rsp->name, rnp->level,

						  rnp->grplo, rnp->grphi,

						  TPS("wait"));

			wait_event(rnp->exp_wq[(s >> 1) & 0x3],

				   sync_exp_work_done(rsp,

						      &rdp->exp_workdone2, s));

			return true;

		}

		rnp->exp_seq_rq = s; /* Followers can wait on us. */

		spin_unlock(&rnp->exp_lock);

		trace_rcu_exp_funnel_lock(rsp->name, rnp->level, rnp->grplo,

					  rnp->grphi, TPS("nxtlvl"));

	}

	mutex_lock(&rsp->exp_mutex);

fastpath:

	if (sync_exp_work_done(rsp, &rdp->exp_workdone3, s)) {

		mutex_unlock(&rsp->exp_mutex);

		return true;

	}

	rcu_exp_gp_seq_start(rsp);

	trace_rcu_exp_grace_period(rsp->name, s, TPS("start"));

	return false;

}



/* Invoked on each online non-idle CPU for expedited quiescent state. */

static void sync_sched_exp_handler(void *data)

{

	struct rcu_data *rdp;

	struct rcu_node *rnp;

	struct rcu_state *rsp = data;



	rdp = this_cpu_ptr(rsp->rda);

	rnp = rdp->mynode;

	if (!(READ_ONCE(rnp->expmask) & rdp->grpmask) ||

	    __this_cpu_read(rcu_sched_data.cpu_no_qs.b.exp))

		return;

	if (rcu_is_cpu_rrupt_from_idle()) {

		rcu_report_exp_rdp(&rcu_sched_state,

				   this_cpu_ptr(&rcu_sched_data), true);

		return;

	}

	__this_cpu_write(rcu_sched_data.cpu_no_qs.b.exp, true);

	resched_cpu(smp_processor_id());

}



/* Send IPI for expedited cleanup if needed at end of CPU-hotplug operation. */

static void sync_sched_exp_online_cleanup(int cpu)

{

	struct rcu_data *rdp;

	int ret;

	struct rcu_node *rnp;

	struct rcu_state *rsp = &rcu_sched_state;



	rdp = per_cpu_ptr(rsp->rda, cpu);

	rnp = rdp->mynode;

	if (!(READ_ONCE(rnp->expmask) & rdp->grpmask))

		return;

	ret = smp_call_function_single(cpu, sync_sched_exp_handler, rsp, 0);

	WARN_ON_ONCE(ret);

}



/*

 * Select the nodes that the upcoming expedited grace period needs

 * to wait for.

 */

static void sync_rcu_exp_select_cpus(struct rcu_state *rsp,

				     smp_call_func_t func)

{

	int cpu;

	unsigned long flags;

	unsigned long mask;

	unsigned long mask_ofl_test;

	unsigned long mask_ofl_ipi;

	int ret;

	struct rcu_node *rnp;



	sync_exp_reset_tree(rsp);

	rcu_for_each_leaf_node(rsp, rnp) {

		raw_spin_lock_irqsave_rcu_node(rnp, flags);



		/* Each pass checks a CPU for identity, offline, and idle. */

		mask_ofl_test = 0;

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

			struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);

			struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);



			if (raw_smp_processor_id() == cpu ||

			    !(atomic_add_return(0, &rdtp->dynticks) & 0x1))

				mask_ofl_test |= rdp->grpmask;

		}

		mask_ofl_ipi = rnp->expmask & ~mask_ofl_test;



		/*

		 * Need to wait for any blocked tasks as well.  Note that

		 * additional blocking tasks will also block the expedited

		 * GP until such time as the ->expmask bits are cleared.

		 */

		if (rcu_preempt_has_tasks(rnp))

			rnp->exp_tasks = rnp->blkd_tasks.next;

		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);



		/* IPI the remaining CPUs for expedited quiescent state. */

		mask = 1;

		for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask <<= 1) {

			if (!(mask_ofl_ipi & mask))

				continue;

retry_ipi:

			ret = smp_call_function_single(cpu, func, rsp, 0);

			if (!ret) {

				mask_ofl_ipi &= ~mask;

				continue;

			}

			/* Failed, raced with offline. */

			raw_spin_lock_irqsave_rcu_node(rnp, flags);

			if (cpu_online(cpu) &&

			    (rnp->expmask & mask)) {

				raw_spin_unlock_irqrestore_rcu_node(rnp, flags);

				schedule_timeout_uninterruptible(1);

				if (cpu_online(cpu) &&

				    (rnp->expmask & mask))

					goto retry_ipi;

				raw_spin_lock_irqsave_rcu_node(rnp, flags);

			}

			if (!(rnp->expmask & mask))

				mask_ofl_ipi &= ~mask;

			raw_spin_unlock_irqrestore_rcu_node(rnp, flags);

		}

		/* Report quiescent states for those that went offline. */

		mask_ofl_test |= mask_ofl_ipi;

		if (mask_ofl_test)

			rcu_report_exp_cpu_mult(rsp, rnp, mask_ofl_test, false);

	}

}



static void synchronize_sched_expedited_wait(struct rcu_state *rsp)

{

	int cpu;

	unsigned long jiffies_stall;

	unsigned long jiffies_start;

	unsigned long mask;

	int ndetected;

	struct rcu_node *rnp;

	struct rcu_node *rnp_root = rcu_get_root(rsp);

	int ret;



	jiffies_stall = rcu_jiffies_till_stall_check();

	jiffies_start = jiffies;



	for (;;) {

		ret = swait_event_timeout(

				rsp->expedited_wq,

				sync_rcu_preempt_exp_done(rnp_root),

				jiffies_stall);

		if (ret > 0 || sync_rcu_preempt_exp_done(rnp_root))

			return;

		if (ret < 0) {

			/* Hit a signal, disable CPU stall warnings. */

			swait_event(rsp->expedited_wq,

				   sync_rcu_preempt_exp_done(rnp_root));

			return;

		}

		pr_err("INFO: %s detected expedited stalls on CPUs/tasks: {",

		       rsp->name);

		ndetected = 0;

		rcu_for_each_leaf_node(rsp, rnp) {

			ndetected += rcu_print_task_exp_stall(rnp);

			mask = 1;

			for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask <<= 1) {

				struct rcu_data *rdp;



				if (!(rnp->expmask & mask))

					continue;

				ndetected++;

				rdp = per_cpu_ptr(rsp->rda, cpu);

				pr_cont(" %d-%c%c%c", cpu,

					"O."[!!cpu_online(cpu)],

					"o."[!!(rdp->grpmask & rnp->expmaskinit)],

					"N."[!!(rdp->grpmask & rnp->expmaskinitnext)]);

			}

			mask <<= 1;

		}

		pr_cont(" } %lu jiffies s: %lu root: %#lx/%c\n",

			jiffies - jiffies_start, rsp->expedited_sequence,

			rnp_root->expmask, ".T"[!!rnp_root->exp_tasks]);

		if (ndetected) {

			pr_err("blocking rcu_node structures:");

			rcu_for_each_node_breadth_first(rsp, rnp) {

				if (rnp == rnp_root)

					continue; /* printed unconditionally */

				if (sync_rcu_preempt_exp_done(rnp))

					continue;

				pr_cont(" l=%u:%d-%d:%#lx/%c",

					rnp->level, rnp->grplo, rnp->grphi,

					rnp->expmask,

					".T"[!!rnp->exp_tasks]);

			}

			pr_cont("\n");

		}

		rcu_for_each_leaf_node(rsp, rnp) {

			mask = 1;

			for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask <<= 1) {

				if (!(rnp->expmask & mask))

					continue;

				dump_cpu_task(cpu);

			}

		}

		jiffies_stall = 3 * rcu_jiffies_till_stall_check() + 3;

	}

}



/*

 * Wait for the current expedited grace period to complete, and then

 * wake up everyone who piggybacked on the just-completed expedited

 * grace period.  Also update all the ->exp_seq_rq counters as needed

 * in order to avoid counter-wrap problems.

 */

static void rcu_exp_wait_wake(struct rcu_state *rsp, unsigned long s)

{

	struct rcu_node *rnp;



	synchronize_sched_expedited_wait(rsp);

	rcu_exp_gp_seq_end(rsp);

	trace_rcu_exp_grace_period(rsp->name, s, TPS("end"));



	/*

	 * Switch over to wakeup mode, allowing the next GP, but -only- the

	 * next GP, to proceed.

	 */

	mutex_lock(&rsp->exp_wake_mutex);

	mutex_unlock(&rsp->exp_mutex);



	rcu_for_each_node_breadth_first(rsp, rnp) {

		if (ULONG_CMP_LT(READ_ONCE(rnp->exp_seq_rq), s)) {

			spin_lock(&rnp->exp_lock);

			/* Recheck, avoid hang in case someone just arrived. */

			if (ULONG_CMP_LT(rnp->exp_seq_rq, s))

				rnp->exp_seq_rq = s;

			spin_unlock(&rnp->exp_lock);

		}

		wake_up_all(&rnp->exp_wq[(rsp->expedited_sequence >> 1) & 0x3]);

	}

	trace_rcu_exp_grace_period(rsp->name, s, TPS("endwake"));

	mutex_unlock(&rsp->exp_wake_mutex);

}



/**

 * synchronize_sched_expedited - Brute-force RCU-sched grace period

 *

 * Wait for an RCU-sched grace period to elapse, but use a "big hammer"

 * approach to force the grace period to end quickly.  This consumes

 * significant time on all CPUs and is unfriendly to real-time workloads,

 * so is thus not recommended for any sort of common-case code.  In fact,

 * if you are using synchronize_sched_expedited() in a loop, please

 * restructure your code to batch your updates, and then use a single

 * synchronize_sched() instead.

 *

 * This implementation can be thought of as an application of sequence

 * locking to expedited grace periods, but using the sequence counter to

 * determine when someone else has already done the work instead of for

 * retrying readers.

 */

void synchronize_sched_expedited(void)

{

	unsigned long s;

	struct rcu_state *rsp = &rcu_sched_state;



	/* If only one CPU, this is automatically a grace period. */

	if (rcu_blocking_is_gp())

		return;



	/* If expedited grace periods are prohibited, fall back to normal. */

	if (rcu_gp_is_normal()) {

		wait_rcu_gp(call_rcu_sched);

		return;

	}



	/* Take a snapshot of the sequence number.  */

	s = rcu_exp_gp_seq_snap(rsp);

	if (exp_funnel_lock(rsp, s))

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



	/* Initialize the rcu_node tree in preparation for the wait. */

	sync_rcu_exp_select_cpus(rsp, sync_sched_exp_handler);



	/* Wait and clean up, including waking everyone. */

	rcu_exp_wait_wake(rsp, s);

}

EXPORT_SYMBOL_GPL(synchronize_sched_expedited);



/*

 * Check to see if there is any immediate RCU-related work to be done

 * by the current CPU, for the specified type of RCU, returning 1 if so.
@@ -4747,4 +4205,5 @@ void __init rcu_init(void) 
		rcu_cpu_notify(NULL, CPU_UP_PREPARE, (void *)(long)cpu);

}



#include "tree_exp.h"

#include "tree_plugin.h"

kernel/rcu/tree_exp.h

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