rcu: Move RCU-related source code to kernel/rcu directory

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 0 insertions, 651 deletions

diff --git a/kernel/srcu.c b/kernel/srcu.c
deleted file mode 100644
index 01d5ccb8bfe3..000000000000
--- a/kernel/srcu.c
+++ /dev/null
@@ -1,651 +0,0 @@
-/*
- * Sleepable Read-Copy Update mechanism for mutual exclusion.
- *
- * This program is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License as published by
- * the Free Software Foundation; either version 2 of the License, or
- * (at your option) any later version.
- *
- * This program is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- * GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License
- * along with this program; if not, write to the Free Software
- * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
- *
- * Copyright (C) IBM Corporation, 2006
- * Copyright (C) Fujitsu, 2012
- *
- * Author: Paul McKenney <paulmck@us.ibm.com>
- *	   Lai Jiangshan <laijs@cn.fujitsu.com>
- *
- * For detailed explanation of Read-Copy Update mechanism see -
- * 		Documentation/RCU/ *.txt
- *
- */
-
-#include <linux/export.h>
-#include <linux/mutex.h>
-#include <linux/percpu.h>
-#include <linux/preempt.h>
-#include <linux/rcupdate.h>
-#include <linux/sched.h>
-#include <linux/smp.h>
-#include <linux/delay.h>
-#include <linux/srcu.h>
-
-#include <trace/events/rcu.h>
-
-#include "rcu.h"
-
-/*
- * Initialize an rcu_batch structure to empty.
- */
-static inline void rcu_batch_init(struct rcu_batch *b)
-{
-	b->head = NULL;
-	b->tail = &b->head;
-}
-
-/*
- * Enqueue a callback onto the tail of the specified rcu_batch structure.
- */
-static inline void rcu_batch_queue(struct rcu_batch *b, struct rcu_head *head)
-{
-	*b->tail = head;
-	b->tail = &head->next;
-}
-
-/*
- * Is the specified rcu_batch structure empty?
- */
-static inline bool rcu_batch_empty(struct rcu_batch *b)
-{
-	return b->tail == &b->head;
-}
-
-/*
- * Remove the callback at the head of the specified rcu_batch structure
- * and return a pointer to it, or return NULL if the structure is empty.
- */
-static inline struct rcu_head *rcu_batch_dequeue(struct rcu_batch *b)
-{
-	struct rcu_head *head;
-
-	if (rcu_batch_empty(b))
-		return NULL;
-
-	head = b->head;
-	b->head = head->next;
-	if (b->tail == &head->next)
-		rcu_batch_init(b);
-
-	return head;
-}
-
-/*
- * Move all callbacks from the rcu_batch structure specified by "from" to
- * the structure specified by "to".
- */
-static inline void rcu_batch_move(struct rcu_batch *to, struct rcu_batch *from)
-{
-	if (!rcu_batch_empty(from)) {
-		*to->tail = from->head;
-		to->tail = from->tail;
-		rcu_batch_init(from);
-	}
-}
-
-static int init_srcu_struct_fields(struct srcu_struct *sp)
-{
-	sp->completed = 0;
-	spin_lock_init(&sp->queue_lock);
-	sp->running = false;
-	rcu_batch_init(&sp->batch_queue);
-	rcu_batch_init(&sp->batch_check0);
-	rcu_batch_init(&sp->batch_check1);
-	rcu_batch_init(&sp->batch_done);
-	INIT_DELAYED_WORK(&sp->work, process_srcu);
-	sp->per_cpu_ref = alloc_percpu(struct srcu_struct_array);
-	return sp->per_cpu_ref ? 0 : -ENOMEM;
-}
-
-#ifdef CONFIG_DEBUG_LOCK_ALLOC
-
-int __init_srcu_struct(struct srcu_struct *sp, const char *name,
-		       struct lock_class_key *key)
-{
-	/* 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);
-	return init_srcu_struct_fields(sp);
-}
-EXPORT_SYMBOL_GPL(__init_srcu_struct);
-
-#else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
-
-/**
- * init_srcu_struct - initialize a sleep-RCU structure
- * @sp: structure to initialize.
- *
- * Must invoke this on a given srcu_struct before passing that srcu_struct
- * to any other function.  Each srcu_struct represents a separate domain
- * of SRCU protection.
- */
-int init_srcu_struct(struct srcu_struct *sp)
-{
-	return init_srcu_struct_fields(sp);
-}
-EXPORT_SYMBOL_GPL(init_srcu_struct);
-
-#endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
-
-/*
- * Returns approximate total of the readers' ->seq[] values for the
- * rank of per-CPU counters specified by idx.
- */
-static unsigned long srcu_readers_seq_idx(struct srcu_struct *sp, int idx)
-{
-	int cpu;
-	unsigned long sum = 0;
-	unsigned long t;
-
-	for_each_possible_cpu(cpu) {
-		t = ACCESS_ONCE(per_cpu_ptr(sp->per_cpu_ref, cpu)->seq[idx]);
-		sum += t;
-	}
-	return sum;
-}
-
-/*
- * Returns approximate number of readers active on the specified rank
- * of the per-CPU ->c[] counters.
- */
-static unsigned long srcu_readers_active_idx(struct srcu_struct *sp, int idx)
-{
-	int cpu;
-	unsigned long sum = 0;
-	unsigned long t;
-
-	for_each_possible_cpu(cpu) {
-		t = ACCESS_ONCE(per_cpu_ptr(sp->per_cpu_ref, cpu)->c[idx]);
-		sum += t;
-	}
-	return sum;
-}
-
-/*
- * Return true if the number of pre-existing readers is determined to
- * be stably zero.  An example unstable zero can occur if the call
- * to srcu_readers_active_idx() misses an __srcu_read_lock() increment,
- * but due to task migration, sees the corresponding __srcu_read_unlock()
- * decrement.  This can happen because srcu_readers_active_idx() takes
- * time to sum the array, and might in fact be interrupted or preempted
- * partway through the summation.
- */
-static bool srcu_readers_active_idx_check(struct srcu_struct *sp, int idx)
-{
-	unsigned long seq;
-
-	seq = srcu_readers_seq_idx(sp, idx);
-
-	/*
-	 * The following smp_mb() A pairs with the smp_mb() B located in
-	 * __srcu_read_lock().  This pairing ensures that if an
-	 * __srcu_read_lock() increments its counter after the summation
-	 * in srcu_readers_active_idx(), then the corresponding SRCU read-side
-	 * critical section will see any changes made prior to the start
-	 * of the current SRCU grace period.
-	 *
-	 * Also, if the above call to srcu_readers_seq_idx() saw the
-	 * increment of ->seq[], then the call to srcu_readers_active_idx()
-	 * must see the increment of ->c[].
-	 */
-	smp_mb(); /* A */
-
-	/*
-	 * Note that srcu_readers_active_idx() can incorrectly return
-	 * zero even though there is a pre-existing reader throughout.
-	 * To see this, suppose that task A is in a very long SRCU
-	 * read-side critical section that started on CPU 0, and that
-	 * no other reader exists, so that the sum of the counters
-	 * is equal to one.  Then suppose that task B starts executing
-	 * srcu_readers_active_idx(), summing up to CPU 1, and then that
-	 * task C starts reading on CPU 0, so that its increment is not
-	 * summed, but finishes reading on CPU 2, so that its decrement
-	 * -is- summed.  Then when task B completes its sum, it will
-	 * incorrectly get zero, despite the fact that task A has been
-	 * in its SRCU read-side critical section the whole time.
-	 *
-	 * We therefore do a validation step should srcu_readers_active_idx()
-	 * return zero.
-	 */
-	if (srcu_readers_active_idx(sp, idx) != 0)
-		return false;
-
-	/*
-	 * The remainder of this function is the validation step.
-	 * The following smp_mb() D pairs with the smp_mb() C in
-	 * __srcu_read_unlock().  If the __srcu_read_unlock() was seen
-	 * by srcu_readers_active_idx() above, then any destructive
-	 * operation performed after the grace period will happen after
-	 * the corresponding SRCU read-side critical section.
-	 *
-	 * Note that there can be at most NR_CPUS worth of readers using
-	 * the old index, which is not enough to overflow even a 32-bit
-	 * integer.  (Yes, this does mean that systems having more than
-	 * a billion or so CPUs need to be 64-bit systems.)  Therefore,
-	 * the sum of the ->seq[] counters cannot possibly overflow.
-	 * Therefore, the only way that the return values of the two
-	 * calls to srcu_readers_seq_idx() can be equal is if there were
-	 * no increments of the corresponding rank of ->seq[] counts
-	 * in the interim.  But the missed-increment scenario laid out
-	 * above includes an increment of the ->seq[] counter by
-	 * the corresponding __srcu_read_lock().  Therefore, if this
-	 * scenario occurs, the return values from the two calls to
-	 * srcu_readers_seq_idx() will differ, and thus the validation
-	 * step below suffices.
-	 */
-	smp_mb(); /* D */
-
-	return srcu_readers_seq_idx(sp, idx) == seq;
-}
-
-/**
- * srcu_readers_active - returns approximate number of readers.
- * @sp: which srcu_struct to count active readers (holding srcu_read_lock).
- *
- * Note that this is not an atomic primitive, and can therefore suffer
- * severe errors when invoked on an active srcu_struct.  That said, it
- * can be useful as an error check at cleanup time.
- */
-static int srcu_readers_active(struct srcu_struct *sp)
-{
-	int cpu;
-	unsigned long sum = 0;
-
-	for_each_possible_cpu(cpu) {
-		sum += ACCESS_ONCE(per_cpu_ptr(sp->per_cpu_ref, cpu)->c[0]);
-		sum += ACCESS_ONCE(per_cpu_ptr(sp->per_cpu_ref, cpu)->c[1]);
-	}
-	return sum;
-}
-
-/**
- * cleanup_srcu_struct - deconstruct a sleep-RCU structure
- * @sp: structure to clean up.
- *
- * Must invoke this after you are finished using a given srcu_struct that
- * was initialized via init_srcu_struct(), else you leak memory.
- */
-void cleanup_srcu_struct(struct srcu_struct *sp)
-{
-	if (WARN_ON(srcu_readers_active(sp)))
-		return; /* Leakage unless caller handles error. */
-	free_percpu(sp->per_cpu_ref);
-	sp->per_cpu_ref = NULL;
-}
-EXPORT_SYMBOL_GPL(cleanup_srcu_struct);
-
-/*
- * Counts the new reader in the appropriate per-CPU element of the
- * srcu_struct.  Must be called from process context.
- * Returns an index that must be passed to the matching srcu_read_unlock().
- */
-int __srcu_read_lock(struct srcu_struct *sp)
-{
-	int idx;
-
-	idx = ACCESS_ONCE(sp->completed) & 0x1;
-	preempt_disable();
-	ACCESS_ONCE(this_cpu_ptr(sp->per_cpu_ref)->c[idx]) += 1;
-	smp_mb(); /* B */  /* Avoid leaking the critical section. */
-	ACCESS_ONCE(this_cpu_ptr(sp->per_cpu_ref)->seq[idx]) += 1;
-	preempt_enable();
-	return idx;
-}
-EXPORT_SYMBOL_GPL(__srcu_read_lock);
-
-/*
- * Removes the count for the old reader from the appropriate per-CPU
- * element of the srcu_struct.  Note that this may well be a different
- * CPU than that which was incremented by the corresponding srcu_read_lock().
- * Must be called from process context.
- */
-void __srcu_read_unlock(struct srcu_struct *sp, int idx)
-{
-	smp_mb(); /* C */  /* Avoid leaking the critical section. */
-	this_cpu_dec(sp->per_cpu_ref->c[idx]);
-}
-EXPORT_SYMBOL_GPL(__srcu_read_unlock);
-
-/*
- * We use an adaptive strategy for synchronize_srcu() and especially for
- * synchronize_srcu_expedited().  We spin for a fixed time period
- * (defined below) to allow SRCU readers to exit their read-side critical
- * sections.  If there are still some readers after 10 microseconds,
- * we repeatedly block for 1-millisecond time periods.  This approach
- * has done well in testing, so there is no need for a config parameter.
- */
-#define SRCU_RETRY_CHECK_DELAY		5
-#define SYNCHRONIZE_SRCU_TRYCOUNT	2
-#define SYNCHRONIZE_SRCU_EXP_TRYCOUNT	12
-
-/*
- * @@@ Wait until all pre-existing readers complete.  Such readers
- * will have used the index specified by "idx".
- * the caller should ensures the ->completed is not changed while checking
- * and idx = (->completed & 1) ^ 1
- */
-static bool try_check_zero(struct srcu_struct *sp, int idx, int trycount)
-{
-	for (;;) {
-		if (srcu_readers_active_idx_check(sp, idx))
-			return true;
-		if (--trycount <= 0)
-			return false;
-		udelay(SRCU_RETRY_CHECK_DELAY);
-	}
-}
-
-/*
- * Increment the ->completed counter so that future SRCU readers will
- * use the other rank of the ->c[] and ->seq[] arrays.  This allows
- * us to wait for pre-existing readers in a starvation-free manner.
- */
-static void srcu_flip(struct srcu_struct *sp)
-{
-	sp->completed++;
-}
-
-/*
- * Enqueue an SRCU callback on the specified srcu_struct structure,
- * initiating grace-period processing if it is not already running.
- */
-void call_srcu(struct srcu_struct *sp, struct rcu_head *head,
-		void (*func)(struct rcu_head *head))
-{
-	unsigned long flags;
-
-	head->next = NULL;
-	head->func = func;
-	spin_lock_irqsave(&sp->queue_lock, flags);
-	rcu_batch_queue(&sp->batch_queue, head);
-	if (!sp->running) {
-		sp->running = true;
-		schedule_delayed_work(&sp->work, 0);
-	}
-	spin_unlock_irqrestore(&sp->queue_lock, flags);
-}
-EXPORT_SYMBOL_GPL(call_srcu);
-
-struct rcu_synchronize {
-	struct rcu_head head;
-	struct completion completion;
-};
-
-/*
- * Awaken the corresponding synchronize_srcu() instance now that a
- * grace period has elapsed.
- */
-static void wakeme_after_rcu(struct rcu_head *head)
-{
-	struct rcu_synchronize *rcu;
-
-	rcu = container_of(head, struct rcu_synchronize, head);
-	complete(&rcu->completion);
-}
-
-static void srcu_advance_batches(struct srcu_struct *sp, int trycount);
-static void srcu_reschedule(struct srcu_struct *sp);
-
-/*
- * Helper function for synchronize_srcu() and synchronize_srcu_expedited().
- */
-static void __synchronize_srcu(struct srcu_struct *sp, int trycount)
-{
-	struct rcu_synchronize rcu;
-	struct rcu_head *head = &rcu.head;
-	bool done = false;
-
-	rcu_lockdep_assert(!lock_is_held(&sp->dep_map) &&
-			   !lock_is_held(&rcu_bh_lock_map) &&
-			   !lock_is_held(&rcu_lock_map) &&
-			   !lock_is_held(&rcu_sched_lock_map),
-			   "Illegal synchronize_srcu() in same-type SRCU (or RCU) read-side critical section");
-
-	might_sleep();
-	init_completion(&rcu.completion);
-
-	head->next = NULL;
-	head->func = wakeme_after_rcu;
-	spin_lock_irq(&sp->queue_lock);
-	if (!sp->running) {
-		/* steal the processing owner */
-		sp->running = true;
-		rcu_batch_queue(&sp->batch_check0, head);
-		spin_unlock_irq(&sp->queue_lock);
-
-		srcu_advance_batches(sp, trycount);
-		if (!rcu_batch_empty(&sp->batch_done)) {
-			BUG_ON(sp->batch_done.head != head);
-			rcu_batch_dequeue(&sp->batch_done);
-			done = true;
-		}
-		/* give the processing owner to work_struct */
-		srcu_reschedule(sp);
-	} else {
-		rcu_batch_queue(&sp->batch_queue, head);
-		spin_unlock_irq(&sp->queue_lock);
-	}
-
-	if (!done)
-		wait_for_completion(&rcu.completion);
-}
-
-/**
- * synchronize_srcu - wait for prior SRCU read-side critical-section completion
- * @sp: srcu_struct with which to synchronize.
- *
- * Wait for the count to drain to zero of both indexes. To avoid the
- * possible starvation of synchronize_srcu(), it waits for the count of
- * the index=((->completed & 1) ^ 1) to drain to zero at first,
- * and then flip the completed and wait for the count of the other index.
- *
- * Can block; must be called from process context.
- *
- * Note that it is illegal to call synchronize_srcu() from the corresponding
- * SRCU read-side critical section; doing so will result in deadlock.
- * However, it is perfectly legal to call synchronize_srcu() on one
- * srcu_struct from some other srcu_struct's read-side critical section.
- */
-void synchronize_srcu(struct srcu_struct *sp)
-{
-	__synchronize_srcu(sp, rcu_expedited
-			   ? SYNCHRONIZE_SRCU_EXP_TRYCOUNT
-			   : SYNCHRONIZE_SRCU_TRYCOUNT);
-}
-EXPORT_SYMBOL_GPL(synchronize_srcu);
-
-/**
- * synchronize_srcu_expedited - Brute-force SRCU grace period
- * @sp: srcu_struct with which to synchronize.
- *
- * Wait for an SRCU grace period to elapse, but be more aggressive about
- * spinning rather than blocking when waiting.
- *
- * Note that it is also illegal to call synchronize_srcu_expedited()
- * from the corresponding SRCU read-side critical section;
- * doing so will result in deadlock.  However, it is perfectly legal
- * to call synchronize_srcu_expedited() on one srcu_struct from some
- * other srcu_struct's read-side critical section, as long as
- * the resulting graph of srcu_structs is acyclic.
- */
-void synchronize_srcu_expedited(struct srcu_struct *sp)
-{
-	__synchronize_srcu(sp, SYNCHRONIZE_SRCU_EXP_TRYCOUNT);
-}
-EXPORT_SYMBOL_GPL(synchronize_srcu_expedited);
-
-/**
- * srcu_barrier - Wait until all in-flight call_srcu() callbacks complete.
- */
-void srcu_barrier(struct srcu_struct *sp)
-{
-	synchronize_srcu(sp);
-}
-EXPORT_SYMBOL_GPL(srcu_barrier);
-
-/**
- * srcu_batches_completed - return batches completed.
- * @sp: srcu_struct on which to report batch completion.
- *
- * Report the number of batches, correlated with, but not necessarily
- * precisely the same as, the number of grace periods that have elapsed.
- */
-long srcu_batches_completed(struct srcu_struct *sp)
-{
-	return sp->completed;
-}
-EXPORT_SYMBOL_GPL(srcu_batches_completed);
-
-#define SRCU_CALLBACK_BATCH	10
-#define SRCU_INTERVAL		1
-
-/*
- * Move any new SRCU callbacks to the first stage of the SRCU grace
- * period pipeline.
- */
-static void srcu_collect_new(struct srcu_struct *sp)
-{
-	if (!rcu_batch_empty(&sp->batch_queue)) {
-		spin_lock_irq(&sp->queue_lock);
-		rcu_batch_move(&sp->batch_check0, &sp->batch_queue);
-		spin_unlock_irq(&sp->queue_lock);
-	}
-}
-
-/*
- * Core SRCU state machine.  Advance callbacks from ->batch_check0 to
- * ->batch_check1 and then to ->batch_done as readers drain.
- */
-static void srcu_advance_batches(struct srcu_struct *sp, int trycount)
-{
-	int idx = 1 ^ (sp->completed & 1);
-
-	/*
-	 * Because readers might be delayed for an extended period after
-	 * fetching ->completed for their index, at any point in time there
-	 * might well be readers using both idx=0 and idx=1.  We therefore
-	 * need to wait for readers to clear from both index values before
-	 * invoking a callback.
-	 */
-
-	if (rcu_batch_empty(&sp->batch_check0) &&
-	    rcu_batch_empty(&sp->batch_check1))
-		return; /* no callbacks need to be advanced */
-
-	if (!try_check_zero(sp, idx, trycount))
-		return; /* failed to advance, will try after SRCU_INTERVAL */
-
-	/*
-	 * The callbacks in ->batch_check1 have already done with their
-	 * first zero check and flip back when they were enqueued on
-	 * ->batch_check0 in a previous invocation of srcu_advance_batches().
-	 * (Presumably try_check_zero() returned false during that
-	 * invocation, leaving the callbacks stranded on ->batch_check1.)
-	 * They are therefore ready to invoke, so move them to ->batch_done.
-	 */
-	rcu_batch_move(&sp->batch_done, &sp->batch_check1);
-
-	if (rcu_batch_empty(&sp->batch_check0))
-		return; /* no callbacks need to be advanced */
-	srcu_flip(sp);
-
-	/*
-	 * The callbacks in ->batch_check0 just finished their
-	 * first check zero and flip, so move them to ->batch_check1
-	 * for future checking on the other idx.
-	 */
-	rcu_batch_move(&sp->batch_check1, &sp->batch_check0);
-
-	/*
-	 * SRCU read-side critical sections are normally short, so check
-	 * at least twice in quick succession after a flip.
-	 */
-	trycount = trycount < 2 ? 2 : trycount;
-	if (!try_check_zero(sp, idx^1, trycount))
-		return; /* failed to advance, will try after SRCU_INTERVAL */
-
-	/*
-	 * The callbacks in ->batch_check1 have now waited for all
-	 * pre-existing readers using both idx values.  They are therefore
-	 * ready to invoke, so move them to ->batch_done.
-	 */
-	rcu_batch_move(&sp->batch_done, &sp->batch_check1);
-}
-
-/*
- * Invoke a limited number of SRCU callbacks that have passed through
- * their grace period.  If there are more to do, SRCU will reschedule
- * the workqueue.
- */
-static void srcu_invoke_callbacks(struct srcu_struct *sp)
-{
-	int i;
-	struct rcu_head *head;
-
-	for (i = 0; i < SRCU_CALLBACK_BATCH; i++) {
-		head = rcu_batch_dequeue(&sp->batch_done);
-		if (!head)
-			break;
-		local_bh_disable();
-		head->func(head);
-		local_bh_enable();
-	}
-}
-
-/*
- * Finished one round of SRCU grace period.  Start another if there are
- * more SRCU callbacks queued, otherwise put SRCU into not-running state.
- */
-static void srcu_reschedule(struct srcu_struct *sp)
-{
-	bool pending = true;
-
-	if (rcu_batch_empty(&sp->batch_done) &&
-	    rcu_batch_empty(&sp->batch_check1) &&
-	    rcu_batch_empty(&sp->batch_check0) &&
-	    rcu_batch_empty(&sp->batch_queue)) {
-		spin_lock_irq(&sp->queue_lock);
-		if (rcu_batch_empty(&sp->batch_done) &&
-		    rcu_batch_empty(&sp->batch_check1) &&
-		    rcu_batch_empty(&sp->batch_check0) &&
-		    rcu_batch_empty(&sp->batch_queue)) {
-			sp->running = false;
-			pending = false;
-		}
-		spin_unlock_irq(&sp->queue_lock);
-	}
-
-	if (pending)
-		schedule_delayed_work(&sp->work, SRCU_INTERVAL);
-}
-
-/*
- * This is the work-queue function that handles SRCU grace periods.
- */
-void process_srcu(struct work_struct *work)
-{
-	struct srcu_struct *sp;
-
-	sp = container_of(work, struct srcu_struct, work.work);
-
-	srcu_collect_new(sp);
-	srcu_advance_batches(sp, 1);
-	srcu_invoke_callbacks(sp);
-	srcu_reschedule(sp);
-}
-EXPORT_SYMBOL_GPL(process_srcu);