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@@ -34,10 +34,77 @@
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#include <linux/delay.h>
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#include <linux/srcu.h>
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+/*
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+ * Initialize an rcu_batch structure to empty.
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+ */
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+static inline void rcu_batch_init(struct rcu_batch *b)
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+{
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+ b->head = NULL;
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+ b->tail = &b->head;
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+}
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+
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+/*
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+ * Enqueue a callback onto the tail of the specified rcu_batch structure.
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+ */
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+static inline void rcu_batch_queue(struct rcu_batch *b, struct rcu_head *head)
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+{
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+ *b->tail = head;
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+ b->tail = &head->next;
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+}
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+
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+/*
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+ * Is the specified rcu_batch structure empty?
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+ */
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+static inline bool rcu_batch_empty(struct rcu_batch *b)
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+{
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+ return b->tail == &b->head;
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+}
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+
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+/*
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+ * Remove the callback at the head of the specified rcu_batch structure
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+ * and return a pointer to it, or return NULL if the structure is empty.
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+ */
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+static inline struct rcu_head *rcu_batch_dequeue(struct rcu_batch *b)
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+{
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+ struct rcu_head *head;
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+
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+ if (rcu_batch_empty(b))
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+ return NULL;
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+
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+ head = b->head;
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+ b->head = head->next;
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+ if (b->tail == &head->next)
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+ rcu_batch_init(b);
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+
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+ return head;
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+}
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+
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+/*
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+ * Move all callbacks from the rcu_batch structure specified by "from" to
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+ * the structure specified by "to".
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+ */
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+static inline void rcu_batch_move(struct rcu_batch *to, struct rcu_batch *from)
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+{
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+ if (!rcu_batch_empty(from)) {
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+ *to->tail = from->head;
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+ to->tail = from->tail;
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+ rcu_batch_init(from);
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+ }
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+}
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+
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+/* single-thread state-machine */
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+static void process_srcu(struct work_struct *work);
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+
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static int init_srcu_struct_fields(struct srcu_struct *sp)
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{
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sp->completed = 0;
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- mutex_init(&sp->mutex);
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+ spin_lock_init(&sp->queue_lock);
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+ sp->running = false;
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+ rcu_batch_init(&sp->batch_queue);
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+ rcu_batch_init(&sp->batch_check0);
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+ rcu_batch_init(&sp->batch_check1);
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+ rcu_batch_init(&sp->batch_done);
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+ INIT_DELAYED_WORK(&sp->work, process_srcu);
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sp->per_cpu_ref = alloc_percpu(struct srcu_struct_array);
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return sp->per_cpu_ref ? 0 : -ENOMEM;
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}
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@@ -73,21 +140,116 @@ EXPORT_SYMBOL_GPL(init_srcu_struct);
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#endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
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/*
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- * srcu_readers_active_idx -- returns approximate number of readers
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- * active on the specified rank of per-CPU counters.
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+ * Returns approximate total of the readers' ->seq[] values for the
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+ * rank of per-CPU counters specified by idx.
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*/
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+static unsigned long srcu_readers_seq_idx(struct srcu_struct *sp, int idx)
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+{
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+ int cpu;
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+ unsigned long sum = 0;
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+ unsigned long t;
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-static int srcu_readers_active_idx(struct srcu_struct *sp, int idx)
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+ for_each_possible_cpu(cpu) {
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+ t = ACCESS_ONCE(per_cpu_ptr(sp->per_cpu_ref, cpu)->seq[idx]);
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+ sum += t;
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+ }
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+ return sum;
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+}
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+
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+/*
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+ * Returns approximate number of readers active on the specified rank
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+ * of the per-CPU ->c[] counters.
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+ */
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+static unsigned long srcu_readers_active_idx(struct srcu_struct *sp, int idx)
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{
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int cpu;
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- int sum;
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+ unsigned long sum = 0;
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+ unsigned long t;
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- sum = 0;
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- for_each_possible_cpu(cpu)
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- sum += per_cpu_ptr(sp->per_cpu_ref, cpu)->c[idx];
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+ for_each_possible_cpu(cpu) {
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+ t = ACCESS_ONCE(per_cpu_ptr(sp->per_cpu_ref, cpu)->c[idx]);
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+ sum += t;
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+ }
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return sum;
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}
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+/*
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+ * Return true if the number of pre-existing readers is determined to
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+ * be stably zero. An example unstable zero can occur if the call
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+ * to srcu_readers_active_idx() misses an __srcu_read_lock() increment,
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+ * but due to task migration, sees the corresponding __srcu_read_unlock()
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+ * decrement. This can happen because srcu_readers_active_idx() takes
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+ * time to sum the array, and might in fact be interrupted or preempted
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+ * partway through the summation.
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+ */
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+static bool srcu_readers_active_idx_check(struct srcu_struct *sp, int idx)
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+{
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+ unsigned long seq;
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+
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+ seq = srcu_readers_seq_idx(sp, idx);
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+
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+ /*
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+ * The following smp_mb() A pairs with the smp_mb() B located in
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+ * __srcu_read_lock(). This pairing ensures that if an
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+ * __srcu_read_lock() increments its counter after the summation
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+ * in srcu_readers_active_idx(), then the corresponding SRCU read-side
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+ * critical section will see any changes made prior to the start
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+ * of the current SRCU grace period.
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+ *
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+ * Also, if the above call to srcu_readers_seq_idx() saw the
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+ * increment of ->seq[], then the call to srcu_readers_active_idx()
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+ * must see the increment of ->c[].
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+ */
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+ smp_mb(); /* A */
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+
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+ /*
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+ * Note that srcu_readers_active_idx() can incorrectly return
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+ * zero even though there is a pre-existing reader throughout.
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+ * To see this, suppose that task A is in a very long SRCU
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+ * read-side critical section that started on CPU 0, and that
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+ * no other reader exists, so that the sum of the counters
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+ * is equal to one. Then suppose that task B starts executing
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+ * srcu_readers_active_idx(), summing up to CPU 1, and then that
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+ * task C starts reading on CPU 0, so that its increment is not
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+ * summed, but finishes reading on CPU 2, so that its decrement
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+ * -is- summed. Then when task B completes its sum, it will
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+ * incorrectly get zero, despite the fact that task A has been
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+ * in its SRCU read-side critical section the whole time.
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+ *
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+ * We therefore do a validation step should srcu_readers_active_idx()
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+ * return zero.
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+ */
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+ if (srcu_readers_active_idx(sp, idx) != 0)
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+ return false;
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+
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+ /*
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+ * The remainder of this function is the validation step.
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+ * The following smp_mb() D pairs with the smp_mb() C in
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+ * __srcu_read_unlock(). If the __srcu_read_unlock() was seen
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+ * by srcu_readers_active_idx() above, then any destructive
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+ * operation performed after the grace period will happen after
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+ * the corresponding SRCU read-side critical section.
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+ *
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+ * Note that there can be at most NR_CPUS worth of readers using
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+ * the old index, which is not enough to overflow even a 32-bit
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+ * integer. (Yes, this does mean that systems having more than
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+ * a billion or so CPUs need to be 64-bit systems.) Therefore,
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+ * the sum of the ->seq[] counters cannot possibly overflow.
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+ * Therefore, the only way that the return values of the two
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+ * calls to srcu_readers_seq_idx() can be equal is if there were
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+ * no increments of the corresponding rank of ->seq[] counts
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+ * in the interim. But the missed-increment scenario laid out
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+ * above includes an increment of the ->seq[] counter by
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+ * the corresponding __srcu_read_lock(). Therefore, if this
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+ * scenario occurs, the return values from the two calls to
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+ * srcu_readers_seq_idx() will differ, and thus the validation
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+ * step below suffices.
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+ */
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+ smp_mb(); /* D */
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+
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+ return srcu_readers_seq_idx(sp, idx) == seq;
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+}
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+
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/**
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* srcu_readers_active - returns approximate number of readers.
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* @sp: which srcu_struct to count active readers (holding srcu_read_lock).
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@@ -98,7 +260,14 @@ static int srcu_readers_active_idx(struct srcu_struct *sp, int idx)
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*/
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static int srcu_readers_active(struct srcu_struct *sp)
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{
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- return srcu_readers_active_idx(sp, 0) + srcu_readers_active_idx(sp, 1);
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+ int cpu;
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+ unsigned long sum = 0;
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+
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+ for_each_possible_cpu(cpu) {
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+ sum += ACCESS_ONCE(per_cpu_ptr(sp->per_cpu_ref, cpu)->c[0]);
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+ sum += ACCESS_ONCE(per_cpu_ptr(sp->per_cpu_ref, cpu)->c[1]);
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+ }
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+ return sum;
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}
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/**
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@@ -131,10 +300,11 @@ int __srcu_read_lock(struct srcu_struct *sp)
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int idx;
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preempt_disable();
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- idx = sp->completed & 0x1;
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- barrier(); /* ensure compiler looks -once- at sp->completed. */
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- per_cpu_ptr(sp->per_cpu_ref, smp_processor_id())->c[idx]++;
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- srcu_barrier(); /* ensure compiler won't misorder critical section. */
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+ idx = rcu_dereference_index_check(sp->completed,
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+ rcu_read_lock_sched_held()) & 0x1;
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+ ACCESS_ONCE(this_cpu_ptr(sp->per_cpu_ref)->c[idx]) += 1;
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+ smp_mb(); /* B */ /* Avoid leaking the critical section. */
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+ ACCESS_ONCE(this_cpu_ptr(sp->per_cpu_ref)->seq[idx]) += 1;
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preempt_enable();
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return idx;
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}
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@@ -149,8 +319,8 @@ EXPORT_SYMBOL_GPL(__srcu_read_lock);
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void __srcu_read_unlock(struct srcu_struct *sp, int idx)
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{
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preempt_disable();
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- srcu_barrier(); /* ensure compiler won't misorder critical section. */
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- per_cpu_ptr(sp->per_cpu_ref, smp_processor_id())->c[idx]--;
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+ smp_mb(); /* C */ /* Avoid leaking the critical section. */
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+ ACCESS_ONCE(this_cpu_ptr(sp->per_cpu_ref)->c[idx]) -= 1;
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preempt_enable();
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}
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EXPORT_SYMBOL_GPL(__srcu_read_unlock);
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@@ -163,106 +333,119 @@ EXPORT_SYMBOL_GPL(__srcu_read_unlock);
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* we repeatedly block for 1-millisecond time periods. This approach
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* has done well in testing, so there is no need for a config parameter.
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*/
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-#define SYNCHRONIZE_SRCU_READER_DELAY 10
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+#define SRCU_RETRY_CHECK_DELAY 5
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+#define SYNCHRONIZE_SRCU_TRYCOUNT 2
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+#define SYNCHRONIZE_SRCU_EXP_TRYCOUNT 12
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/*
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- * Helper function for synchronize_srcu() and synchronize_srcu_expedited().
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+ * @@@ Wait until all pre-existing readers complete. Such readers
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+ * will have used the index specified by "idx".
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+ * the caller should ensures the ->completed is not changed while checking
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+ * and idx = (->completed & 1) ^ 1
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*/
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-static void __synchronize_srcu(struct srcu_struct *sp, void (*sync_func)(void))
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+static bool try_check_zero(struct srcu_struct *sp, int idx, int trycount)
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{
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- int idx;
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-
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- rcu_lockdep_assert(!lock_is_held(&sp->dep_map) &&
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- !lock_is_held(&rcu_bh_lock_map) &&
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- !lock_is_held(&rcu_lock_map) &&
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- !lock_is_held(&rcu_sched_lock_map),
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- "Illegal synchronize_srcu() in same-type SRCU (or RCU) read-side critical section");
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-
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- idx = sp->completed;
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- mutex_lock(&sp->mutex);
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+ for (;;) {
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+ if (srcu_readers_active_idx_check(sp, idx))
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+ return true;
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+ if (--trycount <= 0)
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+ return false;
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+ udelay(SRCU_RETRY_CHECK_DELAY);
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+ }
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+}
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- /*
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- * Check to see if someone else did the work for us while we were
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- * waiting to acquire the lock. We need -two- advances of
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- * the counter, not just one. If there was but one, we might have
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- * shown up -after- our helper's first synchronize_sched(), thus
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- * having failed to prevent CPU-reordering races with concurrent
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- * srcu_read_unlock()s on other CPUs (see comment below). So we
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- * either (1) wait for two or (2) supply the second ourselves.
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- */
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+/*
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+ * Increment the ->completed counter so that future SRCU readers will
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+ * use the other rank of the ->c[] and ->seq[] arrays. This allows
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+ * us to wait for pre-existing readers in a starvation-free manner.
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+ */
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+static void srcu_flip(struct srcu_struct *sp)
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+{
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+ sp->completed++;
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+}
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- if ((sp->completed - idx) >= 2) {
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- mutex_unlock(&sp->mutex);
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- return;
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+/*
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+ * Enqueue an SRCU callback on the specified srcu_struct structure,
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+ * initiating grace-period processing if it is not already running.
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+ */
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+void call_srcu(struct srcu_struct *sp, struct rcu_head *head,
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+ void (*func)(struct rcu_head *head))
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+{
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+ unsigned long flags;
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+
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+ head->next = NULL;
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+ head->func = func;
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+ spin_lock_irqsave(&sp->queue_lock, flags);
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+ rcu_batch_queue(&sp->batch_queue, head);
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+ if (!sp->running) {
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+ sp->running = true;
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+ queue_delayed_work(system_nrt_wq, &sp->work, 0);
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}
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+ spin_unlock_irqrestore(&sp->queue_lock, flags);
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+}
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+EXPORT_SYMBOL_GPL(call_srcu);
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- sync_func(); /* Force memory barrier on all CPUs. */
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+struct rcu_synchronize {
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+ struct rcu_head head;
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+ struct completion completion;
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+};
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- /*
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- * The preceding synchronize_sched() ensures that any CPU that
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- * sees the new value of sp->completed will also see any preceding
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- * changes to data structures made by this CPU. This prevents
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- * some other CPU from reordering the accesses in its SRCU
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- * read-side critical section to precede the corresponding
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- * srcu_read_lock() -- ensuring that such references will in
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- * fact be protected.
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- *
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- * So it is now safe to do the flip.
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- */
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+/*
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+ * Awaken the corresponding synchronize_srcu() instance now that a
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+ * grace period has elapsed.
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+ */
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+static void wakeme_after_rcu(struct rcu_head *head)
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+{
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+ struct rcu_synchronize *rcu;
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- idx = sp->completed & 0x1;
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- sp->completed++;
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+ rcu = container_of(head, struct rcu_synchronize, head);
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+ complete(&rcu->completion);
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+}
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- sync_func(); /* Force memory barrier on all CPUs. */
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+static void srcu_advance_batches(struct srcu_struct *sp, int trycount);
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+static void srcu_reschedule(struct srcu_struct *sp);
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- /*
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- * At this point, because of the preceding synchronize_sched(),
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- * all srcu_read_lock() calls using the old counters have completed.
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- * Their corresponding critical sections might well be still
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- * executing, but the srcu_read_lock() primitives themselves
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- * will have finished executing. We initially give readers
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- * an arbitrarily chosen 10 microseconds to get out of their
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- * SRCU read-side critical sections, then loop waiting 1/HZ
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- * seconds per iteration. The 10-microsecond value has done
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- * very well in testing.
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- */
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-
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- if (srcu_readers_active_idx(sp, idx))
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- udelay(SYNCHRONIZE_SRCU_READER_DELAY);
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- while (srcu_readers_active_idx(sp, idx))
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- schedule_timeout_interruptible(1);
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+/*
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+ * Helper function for synchronize_srcu() and synchronize_srcu_expedited().
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+ */
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+static void __synchronize_srcu(struct srcu_struct *sp, int trycount)
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+{
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+ struct rcu_synchronize rcu;
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+ 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
|
|
|
@@ -309,10 +485,19 @@ 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.
|
|
|
@@ -320,9 +505,146 @@ EXPORT_SYMBOL_GPL(synchronize_srcu_expedited);
|
|
|
* 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);
|
|
|
+}
|
Paul E. McKenney