1 files changed, 435 insertions, 113 deletions

diff --git a/kernel/srcu.c b/kernel/srcu.c
index ba35f3a4a1f4..2095be3318d5 100644
--- a/kernel/srcu.c
+++ b/kernel/srcu.c
@@ -34,10 +34,77 @@
 #include <linux/delay.h>
 #include <linux/srcu.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);
+        }
+}
+
+/* single-thread state-machine */
+static void process_srcu(struct work_struct *work);
+
 static int init_srcu_struct_fields(struct srcu_struct *sp)
 {
         sp->completed = 0;
-        mutex_init(&sp->mutex);
+        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;
 }
@@ -73,21 +140,116 @@ EXPORT_SYMBOL_GPL(init_srcu_struct);
 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
 
 /*
- * srcu_readers_active_idx -- returns approximate number of readers
- *      active on the specified rank of per-CPU counters.
+ * 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;
 
-static int srcu_readers_active_idx(struct srcu_struct *sp, int idx)
+        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;
-        int sum;
+        unsigned long sum = 0;
+        unsigned long t;
 
-        sum = 0;
-        for_each_possible_cpu(cpu)
-                sum += per_cpu_ptr(sp->per_cpu_ref, cpu)->c[idx];
+        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).
@@ -98,7 +260,14 @@ static int srcu_readers_active_idx(struct srcu_struct *sp, int idx)
  */
 static int srcu_readers_active(struct srcu_struct *sp)
 {
-        return srcu_readers_active_idx(sp, 0) + srcu_readers_active_idx(sp, 1);
+        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;
 }
 
 /**
@@ -131,10 +300,11 @@ int __srcu_read_lock(struct srcu_struct *sp)
         int idx;
 
         preempt_disable();
-        idx = sp->completed & 0x1;
-        barrier();  /* ensure compiler looks -once- at sp->completed. */
-        per_cpu_ptr(sp->per_cpu_ref, smp_processor_id())->c[idx]++;
-        srcu_barrier();  /* ensure compiler won't misorder critical section. */
+        idx = rcu_dereference_index_check(sp->completed,
+                                          rcu_read_lock_sched_held()) & 0x1;
+        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;
 }
@@ -149,8 +319,8 @@ EXPORT_SYMBOL_GPL(__srcu_read_lock);
 void __srcu_read_unlock(struct srcu_struct *sp, int idx)
 {
         preempt_disable();
-        srcu_barrier();  /* ensure compiler won't misorder critical section. */
-        per_cpu_ptr(sp->per_cpu_ref, smp_processor_id())->c[idx]--;
+        smp_mb(); /* C */  /* Avoid leaking the critical section. */
+        ACCESS_ONCE(this_cpu_ptr(sp->per_cpu_ref)->c[idx]) -= 1;
         preempt_enable();
 }
 EXPORT_SYMBOL_GPL(__srcu_read_unlock);
@@ -163,106 +333,119 @@ EXPORT_SYMBOL_GPL(__srcu_read_unlock);
  * 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 SYNCHRONIZE_SRCU_READER_DELAY 10
+#define SRCU_RETRY_CHECK_DELAY          5
+#define SYNCHRONIZE_SRCU_TRYCOUNT       2
+#define SYNCHRONIZE_SRCU_EXP_TRYCOUNT   12
 
 /*
- * Helper function for synchronize_srcu() and synchronize_srcu_expedited().
+ * @@@ 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 void __synchronize_srcu(struct srcu_struct *sp, void (*sync_func)(void))
+static bool try_check_zero(struct srcu_struct *sp, int idx, int trycount)
 {
-        int idx;
-
-        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");
-
-        idx = sp->completed;
-        mutex_lock(&sp->mutex);
+        for (;;) {
+                if (srcu_readers_active_idx_check(sp, idx))
+                        return true;
+                if (--trycount <= 0)
+                        return false;
+                udelay(SRCU_RETRY_CHECK_DELAY);
+        }
+}
 
-        /*
-         * Check to see if someone else did the work for us while we were
-         * waiting to acquire the lock.  We need -two- advances of
-         * the counter, not just one.  If there was but one, we might have
-         * shown up -after- our helper's first synchronize_sched(), thus
-         * having failed to prevent CPU-reordering races with concurrent
-         * srcu_read_unlock()s on other CPUs (see comment below).  So we
-         * either (1) wait for two or (2) supply the second ourselves.
-         */
+/*
+ * 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++;
+}
 
-        if ((sp->completed - idx) >= 2) {
-                mutex_unlock(&sp->mutex);
-                return;
+/*
+ * 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;
+                queue_delayed_work(system_nrt_wq, &sp->work, 0);
         }
+        spin_unlock_irqrestore(&sp->queue_lock, flags);
+}
+EXPORT_SYMBOL_GPL(call_srcu);
 
-        sync_func();  /* Force memory barrier on all CPUs. */
+struct rcu_synchronize {
+        struct rcu_head head;
+        struct completion completion;
+};
 
-        /*
-         * The preceding synchronize_sched() ensures that any CPU that
-         * sees the new value of sp->completed will also see any preceding
-         * changes to data structures made by this CPU.  This prevents
-         * some other CPU from reordering the accesses in its SRCU
-         * read-side critical section to precede the corresponding
-         * srcu_read_lock() -- ensuring that such references will in
-         * fact be protected.
-         *
-         * So it is now safe to do the flip.
-         */
+/*
+ * 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;
 
-        idx = sp->completed & 0x1;
-        sp->completed++;
+        rcu = container_of(head, struct rcu_synchronize, head);
+        complete(&rcu->completion);
+}
 
-        sync_func();  /* Force memory barrier on all CPUs. */
+static void srcu_advance_batches(struct srcu_struct *sp, int trycount);
+static void srcu_reschedule(struct srcu_struct *sp);
 
-        /*
-         * At this point, because of the preceding synchronize_sched(),
-         * all srcu_read_lock() calls using the old counters have completed.
-         * Their corresponding critical sections might well be still
-         * executing, but the srcu_read_lock() primitives themselves
-         * will have finished executing.  We initially give readers
-         * an arbitrarily chosen 10 microseconds to get out of their
-         * SRCU read-side critical sections, then loop waiting 1/HZ
-         * seconds per iteration.  The 10-microsecond value has done
-         * very well in testing.
-         */
-
-        if (srcu_readers_active_idx(sp, idx))
-                udelay(SYNCHRONIZE_SRCU_READER_DELAY);
-        while (srcu_readers_active_idx(sp, idx))
-                schedule_timeout_interruptible(1);
+/*
+ * 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;
 
-        sync_func();  /* Force memory barrier on all CPUs. */
+        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");
 
-        /*
-         * The preceding synchronize_sched() forces all srcu_read_unlock()
-         * primitives that were executing concurrently with the preceding
-         * for_each_possible_cpu() loop to have completed by this point.
-         * More importantly, it also forces the corresponding SRCU read-side
-         * critical sections to have also completed, and the corresponding
-         * references to SRCU-protected data items to be dropped.
-         *
-         * Note:
-         *
-         *      Despite what you might think at first glance, the
-         *      preceding synchronize_sched() -must- be within the
-         *      critical section ended by the following mutex_unlock().
-         *      Otherwise, a task taking the early exit can race
-         *      with a srcu_read_unlock(), which might have executed
-         *      just before the preceding srcu_readers_active() check,
-         *      and whose CPU might have reordered the srcu_read_unlock()
-         *      with the preceding critical section.  In this case, there
-         *      is nothing preventing the synchronize_sched() task that is
-         *      taking the early exit from freeing a data structure that
-         *      is still being referenced (out of order) by the task
-         *      doing the srcu_read_unlock().
-         *
-         *      Alternatively, the comparison with "2" on the early exit
-         *      could be changed to "3", but this increases synchronize_srcu()
-         *      latency for bulk loads.  So the current code is preferred.
-         */
+        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);
+        }
 
-        mutex_unlock(&sp->mutex);
+        if (!done)
+                wait_for_completion(&rcu.completion);
 }
 
 /**
@@ -281,7 +464,7 @@ static void __synchronize_srcu(struct srcu_struct *sp, void (*sync_func)(void))
  */
 void synchronize_srcu(struct srcu_struct *sp)
 {
-        __synchronize_srcu(sp, synchronize_sched);
+        __synchronize_srcu(sp, SYNCHRONIZE_SRCU_TRYCOUNT);
 }
 EXPORT_SYMBOL_GPL(synchronize_srcu);
 
@@ -289,18 +472,11 @@ 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 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_srcu_expedited() in a loop, please
- * restructure your code to batch your updates, and then use a single
- * synchronize_srcu() instead.
+ * Wait for an SRCU grace period to elapse, but be more aggressive about
+ * spinning rather than blocking when waiting.
  *
  * Note that it is illegal to call this function while holding any lock
- * that is acquired by a CPU-hotplug notifier.  And yes, it is also illegal
- * to call this function from a CPU-hotplug notifier.  Failing to observe
- * these restriction will result in deadlock.  It is also illegal to call
+ * that is acquired by a CPU-hotplug notifier.  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
@@ -309,20 +485,166 @@ EXPORT_SYMBOL_GPL(synchronize_srcu);
  */
 void synchronize_srcu_expedited(struct srcu_struct *sp)
 {
-        __synchronize_srcu(sp, synchronize_sched_expedited);
+        __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)
+                queue_delayed_work(system_nrt_wq, &sp->work, SRCU_INTERVAL);
+}
+
+/*
+ * This is the work-queue function that handles SRCU grace periods.
+ */
+static 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);
+}