+/*
+ * ring_buffer_frontend.c
+ *
+ * (C) Copyright 2005-2010 - Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
+ *
+ * Ring buffer wait-free buffer synchronization. Producer-consumer and flight
+ * recorder (overwrite) modes. See thesis:
+ *
+ * Desnoyers, Mathieu (2009), "Low-Impact Operating System Tracing", Ph.D.
+ * dissertation, Ecole Polytechnique de Montreal.
+ * http://www.lttng.org/pub/thesis/desnoyers-dissertation-2009-12.pdf
+ *
+ * - Algorithm presentation in Chapter 5:
+ * "Lockless Multi-Core High-Throughput Buffering".
+ * - Algorithm formal verification in Section 8.6:
+ * "Formal verification of LTTng"
+ *
+ * Author:
+ * Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
+ *
+ * Inspired from LTT and RelayFS:
+ * Karim Yaghmour <karim@opersys.com>
+ * Tom Zanussi <zanussi@us.ibm.com>
+ * Bob Wisniewski <bob@watson.ibm.com>
+ * And from K42 :
+ * Bob Wisniewski <bob@watson.ibm.com>
+ *
+ * Buffer reader semantic :
+ *
+ * - get_subbuf_size
+ * while buffer is not finalized and empty
+ * - get_subbuf
+ * - if return value != 0, continue
+ * - splice one subbuffer worth of data to a pipe
+ * - splice the data from pipe to disk/network
+ * - put_subbuf
+ *
+ * Dual LGPL v2.1/GPL v2 license.
+ */
+
+#include <linux/delay.h>
+#include <linux/module.h>
+#include <linux/percpu.h>
+
+#include "../../wrapper/ringbuffer/config.h"
+#include "../../wrapper/ringbuffer/backend.h"
+#include "../../wrapper/ringbuffer/frontend.h"
+#include "../../wrapper/ringbuffer/iterator.h"
+#include "../../wrapper/ringbuffer/nohz.h"
+
+/*
+ * Internal structure representing offsets to use at a sub-buffer switch.
+ */
+struct switch_offsets {
+ unsigned long begin, end, old;
+ size_t pre_header_padding, size;
+ unsigned int switch_new_start:1, switch_new_end:1, switch_old_start:1,
+ switch_old_end:1;
+};
+
+#ifdef CONFIG_NO_HZ
+enum tick_nohz_val {
+ TICK_NOHZ_STOP,
+ TICK_NOHZ_FLUSH,
+ TICK_NOHZ_RESTART,
+};
+
+static ATOMIC_NOTIFIER_HEAD(tick_nohz_notifier);
+#endif /* CONFIG_NO_HZ */
+
+static DEFINE_PER_CPU(spinlock_t, ring_buffer_nohz_lock);
+
+DEFINE_PER_CPU(unsigned int, lib_ring_buffer_nesting);
+EXPORT_PER_CPU_SYMBOL(lib_ring_buffer_nesting);
+
+static
+void lib_ring_buffer_print_errors(struct channel *chan,
+ struct lib_ring_buffer *buf, int cpu);
+
+/*
+ * Must be called under cpu hotplug protection.
+ */
+void lib_ring_buffer_free(struct lib_ring_buffer *buf)
+{
+ struct channel *chan = buf->backend.chan;
+
+ lib_ring_buffer_print_errors(chan, buf, buf->backend.cpu);
+ kfree(buf->commit_hot);
+ kfree(buf->commit_cold);
+
+ lib_ring_buffer_backend_free(&buf->backend);
+}
+
+/**
+ * lib_ring_buffer_reset - Reset ring buffer to initial values.
+ * @buf: Ring buffer.
+ *
+ * Effectively empty the ring buffer. Should be called when the buffer is not
+ * used for writing. The ring buffer can be opened for reading, but the reader
+ * should not be using the iterator concurrently with reset. The previous
+ * current iterator record is reset.
+ */
+void lib_ring_buffer_reset(struct lib_ring_buffer *buf)
+{
+ struct channel *chan = buf->backend.chan;
+ const struct lib_ring_buffer_config *config = chan->backend.config;
+ unsigned int i;
+
+ /*
+ * Reset iterator first. It will put the subbuffer if it currently holds
+ * it.
+ */
+ lib_ring_buffer_iterator_reset(buf);
+ v_set(config, &buf->offset, 0);
+ for (i = 0; i < chan->backend.num_subbuf; i++) {
+ v_set(config, &buf->commit_hot[i].cc, 0);
+ v_set(config, &buf->commit_hot[i].seq, 0);
+ v_set(config, &buf->commit_cold[i].cc_sb, 0);
+ }
+ atomic_long_set(&buf->consumed, 0);
+ atomic_set(&buf->record_disabled, 0);
+ v_set(config, &buf->last_tsc, 0);
+ lib_ring_buffer_backend_reset(&buf->backend);
+ /* Don't reset number of active readers */
+ v_set(config, &buf->records_lost_full, 0);
+ v_set(config, &buf->records_lost_wrap, 0);
+ v_set(config, &buf->records_lost_big, 0);
+ v_set(config, &buf->records_count, 0);
+ v_set(config, &buf->records_overrun, 0);
+ buf->finalized = 0;
+}
+EXPORT_SYMBOL_GPL(lib_ring_buffer_reset);
+
+/**
+ * channel_reset - Reset channel to initial values.
+ * @chan: Channel.
+ *
+ * Effectively empty the channel. Should be called when the channel is not used
+ * for writing. The channel can be opened for reading, but the reader should not
+ * be using the iterator concurrently with reset. The previous current iterator
+ * record is reset.
+ */
+void channel_reset(struct channel *chan)
+{
+ /*
+ * Reset iterators first. Will put the subbuffer if held for reading.
+ */
+ channel_iterator_reset(chan);
+ atomic_set(&chan->record_disabled, 0);
+ /* Don't reset commit_count_mask, still valid */
+ channel_backend_reset(&chan->backend);
+ /* Don't reset switch/read timer interval */
+ /* Don't reset notifiers and notifier enable bits */
+ /* Don't reset reader reference count */
+}
+EXPORT_SYMBOL_GPL(channel_reset);
+
+/*
+ * Must be called under cpu hotplug protection.
+ */
+int lib_ring_buffer_create(struct lib_ring_buffer *buf,
+ struct channel_backend *chanb, int cpu)
+{
+ const struct lib_ring_buffer_config *config = chanb->config;
+ struct channel *chan = container_of(chanb, struct channel, backend);
+ void *priv = chanb->priv;
+ unsigned int num_subbuf;
+ size_t subbuf_header_size;
+ u64 tsc;
+ int ret;
+
+ /* Test for cpu hotplug */
+ if (buf->backend.allocated)
+ return 0;
+
+ /*
+ * Paranoia: per cpu dynamic allocation is not officially documented as
+ * zeroing the memory, so let's do it here too, just in case.
+ */
+ memset(buf, 0, sizeof(*buf));
+
+ ret = lib_ring_buffer_backend_create(&buf->backend, &chan->backend, cpu);
+ if (ret)
+ return ret;
+
+ buf->commit_hot =
+ kzalloc_node(ALIGN(sizeof(*buf->commit_hot)
+ * chan->backend.num_subbuf,
+ 1 << INTERNODE_CACHE_SHIFT),
+ GFP_KERNEL, cpu_to_node(max(cpu, 0)));
+ if (!buf->commit_hot) {
+ ret = -ENOMEM;
+ goto free_chanbuf;
+ }
+
+ buf->commit_cold =
+ kzalloc_node(ALIGN(sizeof(*buf->commit_cold)
+ * chan->backend.num_subbuf,
+ 1 << INTERNODE_CACHE_SHIFT),
+ GFP_KERNEL, cpu_to_node(max(cpu, 0)));
+ if (!buf->commit_cold) {
+ ret = -ENOMEM;
+ goto free_commit;
+ }
+
+ num_subbuf = chan->backend.num_subbuf;
+ init_waitqueue_head(&buf->read_wait);
+ raw_spin_lock_init(&buf->raw_tick_nohz_spinlock);
+
+ /*
+ * Write the subbuffer header for first subbuffer so we know the total
+ * duration of data gathering.
+ */
+ subbuf_header_size = config->cb.subbuffer_header_size();
+ v_set(config, &buf->offset, subbuf_header_size);
+ subbuffer_id_clear_noref(config, &buf->backend.buf_wsb[0].id);
+ tsc = config->cb.ring_buffer_clock_read(buf->backend.chan);
+ config->cb.buffer_begin(buf, tsc, 0);
+ v_add(config, subbuf_header_size, &buf->commit_hot[0].cc);
+
+ if (config->cb.buffer_create) {
+ ret = config->cb.buffer_create(buf, priv, cpu, chanb->name);
+ if (ret)
+ goto free_init;
+ }
+
+ /*
+ * Ensure the buffer is ready before setting it to allocated and setting
+ * the cpumask.
+ * Used for cpu hotplug vs cpumask iteration.
+ */
+ smp_wmb();
+ buf->backend.allocated = 1;
+
+ if (config->alloc == RING_BUFFER_ALLOC_PER_CPU) {
+ CHAN_WARN_ON(chan, cpumask_test_cpu(cpu,
+ chan->backend.cpumask));
+ cpumask_set_cpu(cpu, chan->backend.cpumask);
+ }
+
+ return 0;
+
+ /* Error handling */
+free_init:
+ kfree(buf->commit_cold);
+free_commit:
+ kfree(buf->commit_hot);
+free_chanbuf:
+ lib_ring_buffer_backend_free(&buf->backend);
+ return ret;
+}
+
+static void switch_buffer_timer(unsigned long data)
+{
+ struct lib_ring_buffer *buf = (struct lib_ring_buffer *)data;
+ struct channel *chan = buf->backend.chan;
+ const struct lib_ring_buffer_config *config = chan->backend.config;
+
+ /*
+ * Only flush buffers periodically if readers are active.
+ */
+ if (atomic_long_read(&buf->active_readers))
+ lib_ring_buffer_switch_slow(buf, SWITCH_ACTIVE);
+
+ if (config->alloc == RING_BUFFER_ALLOC_PER_CPU)
+ mod_timer_pinned(&buf->switch_timer,
+ jiffies + chan->switch_timer_interval);
+ else
+ mod_timer(&buf->switch_timer,
+ jiffies + chan->switch_timer_interval);
+}
+
+/*
+ * Called with ring_buffer_nohz_lock held for per-cpu buffers.
+ */
+static void lib_ring_buffer_start_switch_timer(struct lib_ring_buffer *buf)
+{
+ struct channel *chan = buf->backend.chan;
+ const struct lib_ring_buffer_config *config = chan->backend.config;
+
+ if (!chan->switch_timer_interval || buf->switch_timer_enabled)
+ return;
+ init_timer(&buf->switch_timer);
+ buf->switch_timer.function = switch_buffer_timer;
+ buf->switch_timer.expires = jiffies + chan->switch_timer_interval;
+ buf->switch_timer.data = (unsigned long)buf;
+ if (config->alloc == RING_BUFFER_ALLOC_PER_CPU)
+ add_timer_on(&buf->switch_timer, buf->backend.cpu);
+ else
+ add_timer(&buf->switch_timer);
+ buf->switch_timer_enabled = 1;
+}
+
+/*
+ * Called with ring_buffer_nohz_lock held for per-cpu buffers.
+ */
+static void lib_ring_buffer_stop_switch_timer(struct lib_ring_buffer *buf)
+{
+ struct channel *chan = buf->backend.chan;
+
+ if (!chan->switch_timer_interval || !buf->switch_timer_enabled)
+ return;
+
+ del_timer_sync(&buf->switch_timer);
+ buf->switch_timer_enabled = 0;
+}
+
+/*
+ * Polling timer to check the channels for data.
+ */
+static void read_buffer_timer(unsigned long data)
+{
+ struct lib_ring_buffer *buf = (struct lib_ring_buffer *)data;
+ struct channel *chan = buf->backend.chan;
+ const struct lib_ring_buffer_config *config = chan->backend.config;
+
+ CHAN_WARN_ON(chan, !buf->backend.allocated);
+
+ if (atomic_long_read(&buf->active_readers)
+ && lib_ring_buffer_poll_deliver(config, buf, chan)) {
+ wake_up_interruptible(&buf->read_wait);
+ wake_up_interruptible(&chan->read_wait);
+ }
+
+ if (config->alloc == RING_BUFFER_ALLOC_PER_CPU)
+ mod_timer_pinned(&buf->read_timer,
+ jiffies + chan->read_timer_interval);
+ else
+ mod_timer(&buf->read_timer,
+ jiffies + chan->read_timer_interval);
+}
+
+/*
+ * Called with ring_buffer_nohz_lock held for per-cpu buffers.
+ */
+static void lib_ring_buffer_start_read_timer(struct lib_ring_buffer *buf)
+{
+ struct channel *chan = buf->backend.chan;
+ const struct lib_ring_buffer_config *config = chan->backend.config;
+
+ if (config->wakeup != RING_BUFFER_WAKEUP_BY_TIMER
+ || !chan->read_timer_interval
+ || buf->read_timer_enabled)
+ return;
+
+ init_timer(&buf->read_timer);
+ buf->read_timer.function = read_buffer_timer;
+ buf->read_timer.expires = jiffies + chan->read_timer_interval;
+ buf->read_timer.data = (unsigned long)buf;
+
+ if (config->alloc == RING_BUFFER_ALLOC_PER_CPU)
+ add_timer_on(&buf->read_timer, buf->backend.cpu);
+ else
+ add_timer(&buf->read_timer);
+ buf->read_timer_enabled = 1;
+}
+
+/*
+ * Called with ring_buffer_nohz_lock held for per-cpu buffers.
+ */
+static void lib_ring_buffer_stop_read_timer(struct lib_ring_buffer *buf)
+{
+ struct channel *chan = buf->backend.chan;
+ const struct lib_ring_buffer_config *config = chan->backend.config;
+
+ if (config->wakeup != RING_BUFFER_WAKEUP_BY_TIMER
+ || !chan->read_timer_interval
+ || !buf->read_timer_enabled)
+ return;
+
+ del_timer_sync(&buf->read_timer);
+ /*
+ * do one more check to catch data that has been written in the last
+ * timer period.
+ */
+ if (lib_ring_buffer_poll_deliver(config, buf, chan)) {
+ wake_up_interruptible(&buf->read_wait);
+ wake_up_interruptible(&chan->read_wait);
+ }
+ buf->read_timer_enabled = 0;
+}
+
+#ifdef CONFIG_HOTPLUG_CPU
+/**
+ * lib_ring_buffer_cpu_hp_callback - CPU hotplug callback
+ * @nb: notifier block
+ * @action: hotplug action to take
+ * @hcpu: CPU number
+ *
+ * Returns the success/failure of the operation. (%NOTIFY_OK, %NOTIFY_BAD)
+ */
+static
+int __cpuinit lib_ring_buffer_cpu_hp_callback(struct notifier_block *nb,
+ unsigned long action,
+ void *hcpu)
+{
+ unsigned int cpu = (unsigned long)hcpu;
+ struct channel *chan = container_of(nb, struct channel,
+ cpu_hp_notifier);
+ struct lib_ring_buffer *buf = per_cpu_ptr(chan->backend.buf, cpu);
+ const struct lib_ring_buffer_config *config = chan->backend.config;
+
+ if (!chan->cpu_hp_enable)
+ return NOTIFY_DONE;
+
+ CHAN_WARN_ON(chan, config->alloc == RING_BUFFER_ALLOC_GLOBAL);
+
+ switch (action) {
+ case CPU_DOWN_FAILED:
+ case CPU_DOWN_FAILED_FROZEN:
+ case CPU_ONLINE:
+ case CPU_ONLINE_FROZEN:
+ wake_up_interruptible(&chan->hp_wait);
+ lib_ring_buffer_start_switch_timer(buf);
+ lib_ring_buffer_start_read_timer(buf);
+ return NOTIFY_OK;
+
+ case CPU_DOWN_PREPARE:
+ case CPU_DOWN_PREPARE_FROZEN:
+ lib_ring_buffer_stop_switch_timer(buf);
+ lib_ring_buffer_stop_read_timer(buf);
+ return NOTIFY_OK;
+
+ case CPU_DEAD:
+ case CPU_DEAD_FROZEN:
+ /*
+ * Performing a buffer switch on a remote CPU. Performed by
+ * the CPU responsible for doing the hotunplug after the target
+ * CPU stopped running completely. Ensures that all data
+ * from that remote CPU is flushed.
+ */
+ lib_ring_buffer_switch_slow(buf, SWITCH_ACTIVE);
+ return NOTIFY_OK;
+
+ default:
+ return NOTIFY_DONE;
+ }
+}
+#endif
+
+#if defined(CONFIG_NO_HZ) && defined(CONFIG_LIB_RING_BUFFER)
+/*
+ * For per-cpu buffers, call the reader wakeups before switching the buffer, so
+ * that wake-up-tracing generated events are flushed before going idle (in
+ * tick_nohz). We test if the spinlock is locked to deal with the race where
+ * readers try to sample the ring buffer before we perform the switch. We let
+ * the readers retry in that case. If there is data in the buffer, the wake up
+ * is going to forbid the CPU running the reader thread from going idle.
+ */
+static int notrace ring_buffer_tick_nohz_callback(struct notifier_block *nb,
+ unsigned long val,
+ void *data)
+{
+ struct channel *chan = container_of(nb, struct channel,
+ tick_nohz_notifier);
+ const struct lib_ring_buffer_config *config = chan->backend.config;
+ struct lib_ring_buffer *buf;
+ int cpu = smp_processor_id();
+
+ if (config->alloc != RING_BUFFER_ALLOC_PER_CPU) {
+ /*
+ * We don't support keeping the system idle with global buffers
+ * and streaming active. In order to do so, we would need to
+ * sample a non-nohz-cpumask racelessly with the nohz updates
+ * without adding synchronization overhead to nohz. Leave this
+ * use-case out for now.
+ */
+ return 0;
+ }
+
+ buf = channel_get_ring_buffer(config, chan, cpu);
+ switch (val) {
+ case TICK_NOHZ_FLUSH:
+ raw_spin_lock(&buf->raw_tick_nohz_spinlock);
+ if (config->wakeup == RING_BUFFER_WAKEUP_BY_TIMER
+ && chan->read_timer_interval
+ && atomic_long_read(&buf->active_readers)
+ && (lib_ring_buffer_poll_deliver(config, buf, chan)
+ || lib_ring_buffer_pending_data(config, buf, chan))) {
+ wake_up_interruptible(&buf->read_wait);
+ wake_up_interruptible(&chan->read_wait);
+ }
+ if (chan->switch_timer_interval)
+ lib_ring_buffer_switch_slow(buf, SWITCH_ACTIVE);
+ raw_spin_unlock(&buf->raw_tick_nohz_spinlock);
+ break;
+ case TICK_NOHZ_STOP:
+ spin_lock(&__get_cpu_var(ring_buffer_nohz_lock));
+ lib_ring_buffer_stop_switch_timer(buf);
+ lib_ring_buffer_stop_read_timer(buf);
+ spin_unlock(&__get_cpu_var(ring_buffer_nohz_lock));
+ break;
+ case TICK_NOHZ_RESTART:
+ spin_lock(&__get_cpu_var(ring_buffer_nohz_lock));
+ lib_ring_buffer_start_read_timer(buf);
+ lib_ring_buffer_start_switch_timer(buf);
+ spin_unlock(&__get_cpu_var(ring_buffer_nohz_lock));
+ break;
+ }
+
+ return 0;
+}
+
+void notrace lib_ring_buffer_tick_nohz_flush(void)
+{
+ atomic_notifier_call_chain(&tick_nohz_notifier, TICK_NOHZ_FLUSH,
+ NULL);
+}
+
+void notrace lib_ring_buffer_tick_nohz_stop(void)
+{
+ atomic_notifier_call_chain(&tick_nohz_notifier, TICK_NOHZ_STOP,
+ NULL);
+}
+
+void notrace lib_ring_buffer_tick_nohz_restart(void)
+{
+ atomic_notifier_call_chain(&tick_nohz_notifier, TICK_NOHZ_RESTART,
+ NULL);
+}
+#endif /* defined(CONFIG_NO_HZ) && defined(CONFIG_LIB_RING_BUFFER) */
+
+/*
+ * Holds CPU hotplug.
+ */
+static void channel_unregister_notifiers(struct channel *chan)
+{
+ const struct lib_ring_buffer_config *config = chan->backend.config;
+ int cpu;
+
+ channel_iterator_unregister_notifiers(chan);
+ if (config->alloc == RING_BUFFER_ALLOC_PER_CPU) {
+#ifdef CONFIG_NO_HZ
+ /*
+ * Remove the nohz notifier first, so we are certain we stop
+ * the timers.
+ */
+ atomic_notifier_chain_unregister(&tick_nohz_notifier,
+ &chan->tick_nohz_notifier);
+ /*
+ * ring_buffer_nohz_lock will not be needed below, because
+ * we just removed the notifiers, which were the only source of
+ * concurrency.
+ */
+#endif /* CONFIG_NO_HZ */
+#ifdef CONFIG_HOTPLUG_CPU
+ get_online_cpus();
+ chan->cpu_hp_enable = 0;
+ for_each_online_cpu(cpu) {
+ struct lib_ring_buffer *buf = per_cpu_ptr(chan->backend.buf,
+ cpu);
+ lib_ring_buffer_stop_switch_timer(buf);
+ lib_ring_buffer_stop_read_timer(buf);
+ }
+ put_online_cpus();
+ unregister_cpu_notifier(&chan->cpu_hp_notifier);
+#else
+ for_each_possible_cpu(cpu) {
+ struct lib_ring_buffer *buf = per_cpu_ptr(chan->backend.buf,
+ cpu);
+ lib_ring_buffer_stop_switch_timer(buf);
+ lib_ring_buffer_stop_read_timer(buf);
+ }
+#endif
+ } else {
+ struct lib_ring_buffer *buf = chan->backend.buf;
+
+ lib_ring_buffer_stop_switch_timer(buf);
+ lib_ring_buffer_stop_read_timer(buf);
+ }
+ channel_backend_unregister_notifiers(&chan->backend);
+}
+
+static void channel_free(struct channel *chan)
+{
+ channel_iterator_free(chan);
+ channel_backend_free(&chan->backend);
+ kfree(chan);
+}
+
+/**
+ * channel_create - Create channel.
+ * @config: ring buffer instance configuration
+ * @name: name of the channel
+ * @priv: ring buffer client private data
+ * @buf_addr: pointer the the beginning of the preallocated buffer contiguous
+ * address mapping. It is used only by RING_BUFFER_STATIC
+ * configuration. It can be set to NULL for other backends.
+ * @subbuf_size: subbuffer size
+ * @num_subbuf: number of subbuffers
+ * @switch_timer_interval: Time interval (in us) to fill sub-buffers with
+ * padding to let readers get those sub-buffers.
+ * Used for live streaming.
+ * @read_timer_interval: Time interval (in us) to wake up pending readers.
+ *
+ * Holds cpu hotplug.
+ * Returns NULL on failure.
+ */
+struct channel *channel_create(const struct lib_ring_buffer_config *config,
+ const char *name, void *priv, void *buf_addr,
+ size_t subbuf_size,
+ size_t num_subbuf, unsigned int switch_timer_interval,
+ unsigned int read_timer_interval)
+{
+ int ret, cpu;
+ struct channel *chan;
+
+ if (lib_ring_buffer_check_config(config, switch_timer_interval,
+ read_timer_interval))
+ return NULL;
+
+ chan = kzalloc(sizeof(struct channel), GFP_KERNEL);
+ if (!chan)
+ return NULL;
+
+ ret = channel_backend_init(&chan->backend, name, config, priv,
+ subbuf_size, num_subbuf);
+ if (ret)
+ goto error;
+
+ ret = channel_iterator_init(chan);
+ if (ret)
+ goto error_free_backend;
+
+ chan->commit_count_mask = (~0UL >> chan->backend.num_subbuf_order);
+ chan->switch_timer_interval = usecs_to_jiffies(switch_timer_interval);
+ chan->read_timer_interval = usecs_to_jiffies(read_timer_interval);
+ kref_init(&chan->ref);
+ init_waitqueue_head(&chan->read_wait);
+ init_waitqueue_head(&chan->hp_wait);
+
+ if (config->alloc == RING_BUFFER_ALLOC_PER_CPU) {
+#if defined(CONFIG_NO_HZ) && defined(CONFIG_LIB_RING_BUFFER)
+ /* Only benefit from NO_HZ idle with per-cpu buffers for now. */
+ chan->tick_nohz_notifier.notifier_call =
+ ring_buffer_tick_nohz_callback;
+ chan->tick_nohz_notifier.priority = ~0U;
+ atomic_notifier_chain_register(&tick_nohz_notifier,
+ &chan->tick_nohz_notifier);
+#endif /* defined(CONFIG_NO_HZ) && defined(CONFIG_LIB_RING_BUFFER) */
+
+ /*
+ * In case of non-hotplug cpu, if the ring-buffer is allocated
+ * in early initcall, it will not be notified of secondary cpus.
+ * In that off case, we need to allocate for all possible cpus.
+ */
+#ifdef CONFIG_HOTPLUG_CPU
+ chan->cpu_hp_notifier.notifier_call =
+ lib_ring_buffer_cpu_hp_callback;
+ chan->cpu_hp_notifier.priority = 6;
+ register_cpu_notifier(&chan->cpu_hp_notifier);
+
+ get_online_cpus();
+ for_each_online_cpu(cpu) {
+ struct lib_ring_buffer *buf = per_cpu_ptr(chan->backend.buf,
+ cpu);
+ spin_lock(&per_cpu(ring_buffer_nohz_lock, cpu));
+ lib_ring_buffer_start_switch_timer(buf);
+ lib_ring_buffer_start_read_timer(buf);
+ spin_unlock(&per_cpu(ring_buffer_nohz_lock, cpu));
+ }
+ chan->cpu_hp_enable = 1;
+ put_online_cpus();
+#else
+ for_each_possible_cpu(cpu) {
+ struct lib_ring_buffer *buf = per_cpu_ptr(chan->backend.buf,
+ cpu);
+ spin_lock(&per_cpu(ring_buffer_nohz_lock, cpu));
+ lib_ring_buffer_start_switch_timer(buf);
+ lib_ring_buffer_start_read_timer(buf);
+ spin_unlock(&per_cpu(ring_buffer_nohz_lock, cpu));
+ }
+#endif
+ } else {
+ struct lib_ring_buffer *buf = chan->backend.buf;
+
+ lib_ring_buffer_start_switch_timer(buf);
+ lib_ring_buffer_start_read_timer(buf);
+ }
+
+ return chan;
+
+error_free_backend:
+ channel_backend_free(&chan->backend);
+error:
+ kfree(chan);
+ return NULL;
+}
+EXPORT_SYMBOL_GPL(channel_create);
+
+static
+void channel_release(struct kref *kref)
+{
+ struct channel *chan = container_of(kref, struct channel, ref);
+ channel_free(chan);
+}
+
+/**
+ * channel_destroy - Finalize, wait for q.s. and destroy channel.
+ * @chan: channel to destroy
+ *
+ * Holds cpu hotplug.
+ * Call "destroy" callback, finalize channels, wait for readers to release their
+ * reference, then destroy ring buffer data. Note that when readers have
+ * completed data consumption of finalized channels, get_subbuf() will return
+ * -ENODATA. They should release their handle at that point.
+ * Returns the private data pointer.
+ */
+void *channel_destroy(struct channel *chan)
+{
+ int cpu;
+ const struct lib_ring_buffer_config *config = chan->backend.config;
+ void *priv;
+
+ channel_unregister_notifiers(chan);
+
+ if (config->alloc == RING_BUFFER_ALLOC_PER_CPU) {
+ /*
+ * No need to hold cpu hotplug, because all notifiers have been
+ * unregistered.
+ */
+ for_each_channel_cpu(cpu, chan) {
+ struct lib_ring_buffer *buf = per_cpu_ptr(chan->backend.buf,
+ cpu);
+
+ if (config->cb.buffer_finalize)
+ config->cb.buffer_finalize(buf,
+ chan->backend.priv,
+ cpu);
+ if (buf->backend.allocated)
+ lib_ring_buffer_switch_slow(buf, SWITCH_FLUSH);
+ /*
+ * Perform flush before writing to finalized.
+ */
+ smp_wmb();
+ ACCESS_ONCE(buf->finalized) = 1;
+ wake_up_interruptible(&buf->read_wait);
+ }
+ } else {
+ struct lib_ring_buffer *buf = chan->backend.buf;
+
+ if (config->cb.buffer_finalize)
+ config->cb.buffer_finalize(buf, chan->backend.priv, -1);
+ if (buf->backend.allocated)
+ lib_ring_buffer_switch_slow(buf, SWITCH_FLUSH);
+ /*
+ * Perform flush before writing to finalized.
+ */
+ smp_wmb();
+ ACCESS_ONCE(buf->finalized) = 1;
+ wake_up_interruptible(&buf->read_wait);
+ }
+ ACCESS_ONCE(chan->finalized) = 1;
+ wake_up_interruptible(&chan->hp_wait);
+ wake_up_interruptible(&chan->read_wait);
+ kref_put(&chan->ref, channel_release);
+ priv = chan->backend.priv;
+ return priv;
+}
+EXPORT_SYMBOL_GPL(channel_destroy);
+
+struct lib_ring_buffer *channel_get_ring_buffer(
+ const struct lib_ring_buffer_config *config,
+ struct channel *chan, int cpu)
+{
+ if (config->alloc == RING_BUFFER_ALLOC_GLOBAL)
+ return chan->backend.buf;
+ else
+ return per_cpu_ptr(chan->backend.buf, cpu);
+}
+EXPORT_SYMBOL_GPL(channel_get_ring_buffer);
+
+int lib_ring_buffer_open_read(struct lib_ring_buffer *buf)
+{
+ struct channel *chan = buf->backend.chan;
+
+ if (!atomic_long_add_unless(&buf->active_readers, 1, 1))
+ return -EBUSY;
+ kref_get(&chan->ref);
+ smp_mb__after_atomic_inc();
+ return 0;
+}
+EXPORT_SYMBOL_GPL(lib_ring_buffer_open_read);
+
+void lib_ring_buffer_release_read(struct lib_ring_buffer *buf)
+{
+ struct channel *chan = buf->backend.chan;
+
+ CHAN_WARN_ON(chan, atomic_long_read(&buf->active_readers) != 1);
+ smp_mb__before_atomic_dec();
+ atomic_long_dec(&buf->active_readers);
+ kref_put(&chan->ref, channel_release);
+}
+EXPORT_SYMBOL_GPL(lib_ring_buffer_release_read);
+
+/*
+ * Promote compiler barrier to a smp_mb().
+ * For the specific ring buffer case, this IPI call should be removed if the
+ * architecture does not reorder writes. This should eventually be provided by
+ * a separate architecture-specific infrastructure.
+ */
+static void remote_mb(void *info)
+{
+ smp_mb();
+}
+
+/**
+ * lib_ring_buffer_snapshot - save subbuffer position snapshot (for read)
+ * @buf: ring buffer
+ * @consumed: consumed count indicating the position where to read
+ * @produced: produced count, indicates position when to stop reading
+ *
+ * Returns -ENODATA if buffer is finalized, -EAGAIN if there is currently no
+ * data to read at consumed position, or 0 if the get operation succeeds.
+ * Busy-loop trying to get data if the tick_nohz sequence lock is held.
+ */
+
+int lib_ring_buffer_snapshot(struct lib_ring_buffer *buf,
+ unsigned long *consumed, unsigned long *produced)
+{
+ struct channel *chan = buf->backend.chan;
+ const struct lib_ring_buffer_config *config = chan->backend.config;
+ unsigned long consumed_cur, write_offset;
+ int finalized;
+
+retry:
+ finalized = ACCESS_ONCE(buf->finalized);
+ /*
+ * Read finalized before counters.
+ */
+ smp_rmb();
+ consumed_cur = atomic_long_read(&buf->consumed);
+ /*
+ * No need to issue a memory barrier between consumed count read and
+ * write offset read, because consumed count can only change
+ * concurrently in overwrite mode, and we keep a sequence counter
+ * identifier derived from the write offset to check we are getting
+ * the same sub-buffer we are expecting (the sub-buffers are atomically
+ * "tagged" upon writes, tags are checked upon read).
+ */
+ write_offset = v_read(config, &buf->offset);
+
+ /*
+ * Check that we are not about to read the same subbuffer in
+ * which the writer head is.
+ */
+ if (subbuf_trunc(write_offset, chan) - subbuf_trunc(consumed_cur, chan)
+ == 0)
+ goto nodata;
+
+ *consumed = consumed_cur;
+ *produced = subbuf_trunc(write_offset, chan);
+
+ return 0;
+
+nodata:
+ /*
+ * The memory barriers __wait_event()/wake_up_interruptible() take care
+ * of "raw_spin_is_locked" memory ordering.
+ */
+ if (finalized)
+ return -ENODATA;
+ else if (raw_spin_is_locked(&buf->raw_tick_nohz_spinlock))
+ goto retry;
+ else
+ return -EAGAIN;
+}
+EXPORT_SYMBOL_GPL(lib_ring_buffer_snapshot);
+
+/**
+ * lib_ring_buffer_put_snapshot - move consumed counter forward
+ * @buf: ring buffer
+ * @consumed_new: new consumed count value
+ */
+void lib_ring_buffer_move_consumer(struct lib_ring_buffer *buf,
+ unsigned long consumed_new)
+{
+ struct lib_ring_buffer_backend *bufb = &buf->backend;
+ struct channel *chan = bufb->chan;
+ unsigned long consumed;
+
+ CHAN_WARN_ON(chan, atomic_long_read(&buf->active_readers) != 1);
+
+ /*
+ * Only push the consumed value forward.
+ * If the consumed cmpxchg fails, this is because we have been pushed by
+ * the writer in flight recorder mode.
+ */
+ consumed = atomic_long_read(&buf->consumed);
+ while ((long) consumed - (long) consumed_new < 0)
+ consumed = atomic_long_cmpxchg(&buf->consumed, consumed,
+ consumed_new);
+}
+EXPORT_SYMBOL_GPL(lib_ring_buffer_move_consumer);
+
+/**
+ * lib_ring_buffer_get_subbuf - get exclusive access to subbuffer for reading
+ * @buf: ring buffer
+ * @consumed: consumed count indicating the position where to read
+ *
+ * Returns -ENODATA if buffer is finalized, -EAGAIN if there is currently no
+ * data to read at consumed position, or 0 if the get operation succeeds.
+ * Busy-loop trying to get data if the tick_nohz sequence lock is held.
+ */
+int lib_ring_buffer_get_subbuf(struct lib_ring_buffer *buf,
+ unsigned long consumed)
+{
+ struct channel *chan = buf->backend.chan;
+ const struct lib_ring_buffer_config *config = chan->backend.config;
+ unsigned long consumed_cur, consumed_idx, commit_count, write_offset;
+ int ret;
+ int finalized;
+
+retry:
+ finalized = ACCESS_ONCE(buf->finalized);
+ /*
+ * Read finalized before counters.
+ */
+ smp_rmb();
+ consumed_cur = atomic_long_read(&buf->consumed);
+ consumed_idx = subbuf_index(consumed, chan);
+ commit_count = v_read(config, &buf->commit_cold[consumed_idx].cc_sb);
+ /*
+ * Make sure we read the commit count before reading the buffer
+ * data and the write offset. Correct consumed offset ordering
+ * wrt commit count is insured by the use of cmpxchg to update
+ * the consumed offset.
+ * smp_call_function_single can fail if the remote CPU is offline,
+ * this is OK because then there is no wmb to execute there.
+ * If our thread is executing on the same CPU as the on the buffers
+ * belongs to, we don't have to synchronize it at all. If we are
+ * migrated, the scheduler will take care of the memory barriers.
+ * Normally, smp_call_function_single() should ensure program order when
+ * executing the remote function, which implies that it surrounds the
+ * function execution with :
+ * smp_mb()
+ * send IPI
+ * csd_lock_wait
+ * recv IPI
+ * smp_mb()
+ * exec. function
+ * smp_mb()
+ * csd unlock
+ * smp_mb()
+ *
+ * However, smp_call_function_single() does not seem to clearly execute
+ * such barriers. It depends on spinlock semantic to provide the barrier
+ * before executing the IPI and, when busy-looping, csd_lock_wait only
+ * executes smp_mb() when it has to wait for the other CPU.
+ *
+ * I don't trust this code. Therefore, let's add the smp_mb() sequence
+ * required ourself, even if duplicated. It has no performance impact
+ * anyway.
+ *
+ * smp_mb() is needed because smp_rmb() and smp_wmb() only order read vs
+ * read and write vs write. They do not ensure core synchronization. We
+ * really have to ensure total order between the 3 barriers running on
+ * the 2 CPUs.
+ */
+ if (config->ipi == RING_BUFFER_IPI_BARRIER) {
+ if (config->sync == RING_BUFFER_SYNC_PER_CPU
+ && config->alloc == RING_BUFFER_ALLOC_PER_CPU) {
+ if (raw_smp_processor_id() != buf->backend.cpu) {
+ /* Total order with IPI handler smp_mb() */
+ smp_mb();
+ smp_call_function_single(buf->backend.cpu,
+ remote_mb, NULL, 1);
+ /* Total order with IPI handler smp_mb() */
+ smp_mb();
+ }
+ } else {
+ /* Total order with IPI handler smp_mb() */
+ smp_mb();
+ smp_call_function(remote_mb, NULL, 1);
+ /* Total order with IPI handler smp_mb() */
+ smp_mb();
+ }
+ } else {
+ /*
+ * Local rmb to match the remote wmb to read the commit count
+ * before the buffer data and the write offset.
+ */
+ smp_rmb();
+ }
+
+ write_offset = v_read(config, &buf->offset);
+
+ /*
+ * Check that the buffer we are getting is after or at consumed_cur
+ * position.
+ */
+ if ((long) subbuf_trunc(consumed, chan)
+ - (long) subbuf_trunc(consumed_cur, chan) < 0)
+ goto nodata;
+
+ /*
+ * Check that the subbuffer we are trying to consume has been
+ * already fully committed.
+ */
+ if (((commit_count - chan->backend.subbuf_size)
+ & chan->commit_count_mask)
+ - (buf_trunc(consumed_cur, chan)
+ >> chan->backend.num_subbuf_order)
+ != 0)
+ goto nodata;
+
+ /*
+ * Check that we are not about to read the same subbuffer in
+ * which the writer head is.
+ */
+ if (subbuf_trunc(write_offset, chan) - subbuf_trunc(consumed_cur, chan)
+ == 0)
+ goto nodata;
+
+ /*
+ * Failure to get the subbuffer causes a busy-loop retry without going
+ * to a wait queue. These are caused by short-lived race windows where
+ * the writer is getting access to a subbuffer we were trying to get
+ * access to. Also checks that the "consumed" buffer count we are
+ * looking for matches the one contained in the subbuffer id.
+ */
+ ret = update_read_sb_index(config, &buf->backend, &chan->backend,
+ consumed_idx, buf_trunc_val(consumed, chan));
+ if (ret)
+ goto retry;
+ subbuffer_id_clear_noref(config, &buf->backend.buf_rsb.id);
+
+ buf->get_subbuf_consumed = consumed;
+ buf->get_subbuf = 1;
+
+ return 0;
+
+nodata:
+ /*
+ * The memory barriers __wait_event()/wake_up_interruptible() take care
+ * of "raw_spin_is_locked" memory ordering.
+ */
+ if (finalized)
+ return -ENODATA;
+ else if (raw_spin_is_locked(&buf->raw_tick_nohz_spinlock))
+ goto retry;
+ else
+ return -EAGAIN;
+}
+EXPORT_SYMBOL_GPL(lib_ring_buffer_get_subbuf);
+
+/**
+ * lib_ring_buffer_put_subbuf - release exclusive subbuffer access
+ * @buf: ring buffer
+ */
+void lib_ring_buffer_put_subbuf(struct lib_ring_buffer *buf)
+{
+ struct lib_ring_buffer_backend *bufb = &buf->backend;
+ struct channel *chan = bufb->chan;
+ const struct lib_ring_buffer_config *config = chan->backend.config;
+ unsigned long read_sb_bindex, consumed_idx, consumed;
+
+ CHAN_WARN_ON(chan, atomic_long_read(&buf->active_readers) != 1);
+
+ if (!buf->get_subbuf) {
+ /*
+ * Reader puts a subbuffer it did not get.
+ */
+ CHAN_WARN_ON(chan, 1);
+ return;
+ }
+ consumed = buf->get_subbuf_consumed;
+ buf->get_subbuf = 0;
+
+ /*
+ * Clear the records_unread counter. (overruns counter)
+ * Can still be non-zero if a file reader simply grabbed the data
+ * without using iterators.
+ * Can be below zero if an iterator is used on a snapshot more than
+ * once.
+ */
+ read_sb_bindex = subbuffer_id_get_index(config, bufb->buf_rsb.id);
+ v_add(config, v_read(config,
+ &bufb->array[read_sb_bindex]->records_unread),
+ &bufb->records_read);
+ v_set(config, &bufb->array[read_sb_bindex]->records_unread, 0);
+ CHAN_WARN_ON(chan, config->mode == RING_BUFFER_OVERWRITE
+ && subbuffer_id_is_noref(config, bufb->buf_rsb.id));
+ subbuffer_id_set_noref(config, &bufb->buf_rsb.id);
+
+ /*
+ * Exchange the reader subbuffer with the one we put in its place in the
+ * writer subbuffer table. Expect the original consumed count. If
+ * update_read_sb_index fails, this is because the writer updated the
+ * subbuffer concurrently. We should therefore keep the subbuffer we
+ * currently have: it has become invalid to try reading this sub-buffer
+ * consumed count value anyway.
+ */
+ consumed_idx = subbuf_index(consumed, chan);
+ update_read_sb_index(config, &buf->backend, &chan->backend,
+ consumed_idx, buf_trunc_val(consumed, chan));
+ /*
+ * update_read_sb_index return value ignored. Don't exchange sub-buffer
+ * if the writer concurrently updated it.
+ */
+}
+EXPORT_SYMBOL_GPL(lib_ring_buffer_put_subbuf);
+
+/*
+ * cons_offset is an iterator on all subbuffer offsets between the reader
+ * position and the writer position. (inclusive)
+ */
+static
+void lib_ring_buffer_print_subbuffer_errors(struct lib_ring_buffer *buf,
+ struct channel *chan,
+ unsigned long cons_offset,
+ int cpu)
+{
+ const struct lib_ring_buffer_config *config = chan->backend.config;
+ unsigned long cons_idx, commit_count, commit_count_sb;
+
+ cons_idx = subbuf_index(cons_offset, chan);
+ commit_count = v_read(config, &buf->commit_hot[cons_idx].cc);
+ commit_count_sb = v_read(config, &buf->commit_cold[cons_idx].cc_sb);
+
+ if (subbuf_offset(commit_count, chan) != 0)
+ printk(KERN_WARNING
+ "ring buffer %s, cpu %d: "
+ "commit count in subbuffer %lu,\n"
+ "expecting multiples of %lu bytes\n"
+ " [ %lu bytes committed, %lu bytes reader-visible ]\n",
+ chan->backend.name, cpu, cons_idx,
+ chan->backend.subbuf_size,
+ commit_count, commit_count_sb);
+
+ printk(KERN_DEBUG "ring buffer: %s, cpu %d: %lu bytes committed\n",
+ chan->backend.name, cpu, commit_count);
+}
+
+static
+void lib_ring_buffer_print_buffer_errors(struct lib_ring_buffer *buf,
+ struct channel *chan,
+ void *priv, int cpu)
+{
+ const struct lib_ring_buffer_config *config = chan->backend.config;
+ unsigned long write_offset, cons_offset;
+
+ /*
+ * Can be called in the error path of allocation when
+ * trans_channel_data is not yet set.
+ */
+ if (!chan)
+ return;
+ /*
+ * No need to order commit_count, write_offset and cons_offset reads
+ * because we execute at teardown when no more writer nor reader
+ * references are left.
+ */
+ write_offset = v_read(config, &buf->offset);
+ cons_offset = atomic_long_read(&buf->consumed);
+ if (write_offset != cons_offset)
+ printk(KERN_WARNING
+ "ring buffer %s, cpu %d: "
+ "non-consumed data\n"
+ " [ %lu bytes written, %lu bytes read ]\n",
+ chan->backend.name, cpu, write_offset, cons_offset);
+
+ for (cons_offset = atomic_long_read(&buf->consumed);
+ (long) (subbuf_trunc((unsigned long) v_read(config, &buf->offset),
+ chan)
+ - cons_offset) > 0;
+ cons_offset = subbuf_align(cons_offset, chan))
+ lib_ring_buffer_print_subbuffer_errors(buf, chan, cons_offset,
+ cpu);
+}
+
+static
+void lib_ring_buffer_print_errors(struct channel *chan,
+ struct lib_ring_buffer *buf, int cpu)
+{
+ const struct lib_ring_buffer_config *config = chan->backend.config;
+ void *priv = chan->backend.priv;
+
+ printk(KERN_DEBUG "ring buffer %s, cpu %d: %lu records written, "
+ "%lu records overrun\n",
+ chan->backend.name, cpu,
+ v_read(config, &buf->records_count),
+ v_read(config, &buf->records_overrun));
+
+ if (v_read(config, &buf->records_lost_full)
+ || v_read(config, &buf->records_lost_wrap)
+ || v_read(config, &buf->records_lost_big))
+ printk(KERN_WARNING
+ "ring buffer %s, cpu %d: records were lost. Caused by:\n"
+ " [ %lu buffer full, %lu nest buffer wrap-around, "
+ "%lu event too big ]\n",
+ chan->backend.name, cpu,
+ v_read(config, &buf->records_lost_full),
+ v_read(config, &buf->records_lost_wrap),
+ v_read(config, &buf->records_lost_big));
+
+ lib_ring_buffer_print_buffer_errors(buf, chan, priv, cpu);
+}
+
+/*
+ * lib_ring_buffer_switch_old_start: Populate old subbuffer header.
+ *
+ * Only executed when the buffer is finalized, in SWITCH_FLUSH.
+ */
+static
+void lib_ring_buffer_switch_old_start(struct lib_ring_buffer *buf,
+ struct channel *chan,
+ struct switch_offsets *offsets,
+ u64 tsc)
+{
+ const struct lib_ring_buffer_config *config = chan->backend.config;
+ unsigned long oldidx = subbuf_index(offsets->old, chan);
+ unsigned long commit_count;
+
+ config->cb.buffer_begin(buf, tsc, oldidx);
+
+ /*
+ * Order all writes to buffer before the commit count update that will
+ * determine that the subbuffer is full.
+ */
+ if (config->ipi == RING_BUFFER_IPI_BARRIER) {
+ /*
+ * Must write slot data before incrementing commit count. This
+ * compiler barrier is upgraded into a smp_mb() by the IPI sent
+ * by get_subbuf().
+ */
+ barrier();
+ } else
+ smp_wmb();
+ v_add(config, config->cb.subbuffer_header_size(),
+ &buf->commit_hot[oldidx].cc);
+ commit_count = v_read(config, &buf->commit_hot[oldidx].cc);
+ /* Check if the written buffer has to be delivered */
+ lib_ring_buffer_check_deliver(config, buf, chan, offsets->old,
+ commit_count, oldidx);
+ lib_ring_buffer_write_commit_counter(config, buf, chan, oldidx,
+ offsets->old, commit_count,
+ config->cb.subbuffer_header_size());
+}
+
+/*
+ * lib_ring_buffer_switch_old_end: switch old subbuffer
+ *
+ * Note : offset_old should never be 0 here. It is ok, because we never perform
+ * buffer switch on an empty subbuffer in SWITCH_ACTIVE mode. The caller
+ * increments the offset_old value when doing a SWITCH_FLUSH on an empty
+ * subbuffer.
+ */
+static
+void lib_ring_buffer_switch_old_end(struct lib_ring_buffer *buf,
+ struct channel *chan,
+ struct switch_offsets *offsets,
+ u64 tsc)
+{
+ const struct lib_ring_buffer_config *config = chan->backend.config;
+ unsigned long oldidx = subbuf_index(offsets->old - 1, chan);
+ unsigned long commit_count, padding_size, data_size;
+
+ data_size = subbuf_offset(offsets->old - 1, chan) + 1;
+ padding_size = chan->backend.subbuf_size - data_size;
+ subbuffer_set_data_size(config, &buf->backend, oldidx, data_size);
+
+ /*
+ * Order all writes to buffer before the commit count update that will
+ * determine that the subbuffer is full.
+ */
+ if (config->ipi == RING_BUFFER_IPI_BARRIER) {
+ /*
+ * Must write slot data before incrementing commit count. This
+ * compiler barrier is upgraded into a smp_mb() by the IPI sent
+ * by get_subbuf().
+ */
+ barrier();
+ } else
+ smp_wmb();
+ v_add(config, padding_size, &buf->commit_hot[oldidx].cc);
+ commit_count = v_read(config, &buf->commit_hot[oldidx].cc);
+ lib_ring_buffer_check_deliver(config, buf, chan, offsets->old - 1,
+ commit_count, oldidx);
+ lib_ring_buffer_write_commit_counter(config, buf, chan, oldidx,
+ offsets->old, commit_count,
+ padding_size);
+}
+
+/*
+ * lib_ring_buffer_switch_new_start: Populate new subbuffer.
+ *
+ * This code can be executed unordered : writers may already have written to the
+ * sub-buffer before this code gets executed, caution. The commit makes sure
+ * that this code is executed before the deliver of this sub-buffer.
+ */
+static
+void lib_ring_buffer_switch_new_start(struct lib_ring_buffer *buf,
+ struct channel *chan,
+ struct switch_offsets *offsets,
+ u64 tsc)
+{
+ const struct lib_ring_buffer_config *config = chan->backend.config;
+ unsigned long beginidx = subbuf_index(offsets->begin, chan);
+ unsigned long commit_count;
+
+ config->cb.buffer_begin(buf, tsc, beginidx);
+
+ /*
+ * Order all writes to buffer before the commit count update that will
+ * determine that the subbuffer is full.
+ */
+ if (config->ipi == RING_BUFFER_IPI_BARRIER) {
+ /*
+ * Must write slot data before incrementing commit count. This
+ * compiler barrier is upgraded into a smp_mb() by the IPI sent
+ * by get_subbuf().
+ */
+ barrier();
+ } else
+ smp_wmb();
+ v_add(config, config->cb.subbuffer_header_size(),
+ &buf->commit_hot[beginidx].cc);
+ commit_count = v_read(config, &buf->commit_hot[beginidx].cc);
+ /* Check if the written buffer has to be delivered */
+ lib_ring_buffer_check_deliver(config, buf, chan, offsets->begin,
+ commit_count, beginidx);
+ lib_ring_buffer_write_commit_counter(config, buf, chan, beginidx,
+ offsets->begin, commit_count,
+ config->cb.subbuffer_header_size());
+}
+
+/*
+ * lib_ring_buffer_switch_new_end: finish switching current subbuffer
+ *
+ * The only remaining threads could be the ones with pending commits. They will
+ * have to do the deliver themselves.
+ */
+static
+void lib_ring_buffer_switch_new_end(struct lib_ring_buffer *buf,
+ struct channel *chan,
+ struct switch_offsets *offsets,
+ u64 tsc)
+{
+ const struct lib_ring_buffer_config *config = chan->backend.config;
+ unsigned long endidx = subbuf_index(offsets->end - 1, chan);
+ unsigned long commit_count, padding_size, data_size;
+
+ data_size = subbuf_offset(offsets->end - 1, chan) + 1;
+ padding_size = chan->backend.subbuf_size - data_size;
+ subbuffer_set_data_size(config, &buf->backend, endidx, data_size);
+
+ /*
+ * Order all writes to buffer before the commit count update that will
+ * determine that the subbuffer is full.
+ */
+ if (config->ipi == RING_BUFFER_IPI_BARRIER) {
+ /*
+ * Must write slot data before incrementing commit count. This
+ * compiler barrier is upgraded into a smp_mb() by the IPI sent
+ * by get_subbuf().
+ */
+ barrier();
+ } else
+ smp_wmb();
+ v_add(config, padding_size, &buf->commit_hot[endidx].cc);
+ commit_count = v_read(config, &buf->commit_hot[endidx].cc);
+ lib_ring_buffer_check_deliver(config, buf, chan, offsets->end - 1,
+ commit_count, endidx);
+ lib_ring_buffer_write_commit_counter(config, buf, chan, endidx,
+ offsets->end, commit_count,
+ padding_size);
+}
+
+/*
+ * Returns :
+ * 0 if ok
+ * !0 if execution must be aborted.
+ */
+static
+int lib_ring_buffer_try_switch_slow(enum switch_mode mode,
+ struct lib_ring_buffer *buf,
+ struct channel *chan,
+ struct switch_offsets *offsets,
+ u64 *tsc)
+{
+ const struct lib_ring_buffer_config *config = chan->backend.config;
+ unsigned long off;
+
+ offsets->begin = v_read(config, &buf->offset);
+ offsets->old = offsets->begin;
+ offsets->switch_old_start = 0;
+ off = subbuf_offset(offsets->begin, chan);
+
+ *tsc = config->cb.ring_buffer_clock_read(chan);
+
+ /*
+ * Ensure we flush the header of an empty subbuffer when doing the
+ * finalize (SWITCH_FLUSH). This ensures that we end up knowing the
+ * total data gathering duration even if there were no records saved
+ * after the last buffer switch.
+ * In SWITCH_ACTIVE mode, switch the buffer when it contains events.
+ * SWITCH_ACTIVE only flushes the current subbuffer, dealing with end of
+ * subbuffer header as appropriate.
+ * The next record that reserves space will be responsible for
+ * populating the following subbuffer header. We choose not to populate
+ * the next subbuffer header here because we want to be able to use
+ * SWITCH_ACTIVE for periodical buffer flush and CPU tick_nohz stop
+ * buffer flush, which must guarantee that all the buffer content
+ * (records and header timestamps) are visible to the reader. This is
+ * required for quiescence guarantees for the fusion merge.
+ */
+ if (mode == SWITCH_FLUSH || off > 0) {
+ if (unlikely(off == 0)) {
+ /*
+ * The client does not save any header information.
+ * Don't switch empty subbuffer on finalize, because it
+ * is invalid to deliver a completely empty subbuffer.
+ */
+ if (!config->cb.subbuffer_header_size())
+ return -1;
+ /*
+ * Need to write the subbuffer start header on finalize.
+ */
+ offsets->switch_old_start = 1;
+ }
+ offsets->begin = subbuf_align(offsets->begin, chan);
+ } else
+ return -1; /* we do not have to switch : buffer is empty */
+ /* Note: old points to the next subbuf at offset 0 */
+ offsets->end = offsets->begin;
+ return 0;
+}
+
+/*
+ * Force a sub-buffer switch. This operation is completely reentrant : can be
+ * called while tracing is active with absolutely no lock held.
+ *
+ * Note, however, that as a v_cmpxchg is used for some atomic
+ * operations, this function must be called from the CPU which owns the buffer
+ * for a ACTIVE flush.
+ */
+void lib_ring_buffer_switch_slow(struct lib_ring_buffer *buf, enum switch_mode mode)
+{
+ struct channel *chan = buf->backend.chan;
+ const struct lib_ring_buffer_config *config = chan->backend.config;
+ struct switch_offsets offsets;
+ unsigned long oldidx;
+ u64 tsc;
+
+ offsets.size = 0;
+
+ /*
+ * Perform retryable operations.
+ */
+ do {
+ if (lib_ring_buffer_try_switch_slow(mode, buf, chan, &offsets,
+ &tsc))
+ return; /* Switch not needed */
+ } while (v_cmpxchg(config, &buf->offset, offsets.old, offsets.end)
+ != offsets.old);
+
+ /*
+ * Atomically update last_tsc. This update races against concurrent
+ * atomic updates, but the race will always cause supplementary full TSC
+ * records, never the opposite (missing a full TSC record when it would
+ * be needed).
+ */
+ save_last_tsc(config, buf, tsc);
+
+ /*
+ * Push the reader if necessary
+ */
+ lib_ring_buffer_reserve_push_reader(buf, chan, offsets.old);
+
+ oldidx = subbuf_index(offsets.old, chan);
+ lib_ring_buffer_clear_noref(config, &buf->backend, oldidx);
+
+ /*
+ * May need to populate header start on SWITCH_FLUSH.
+ */
+ if (offsets.switch_old_start) {
+ lib_ring_buffer_switch_old_start(buf, chan, &offsets, tsc);
+ offsets.old += config->cb.subbuffer_header_size();
+ }
+
+ /*
+ * Switch old subbuffer.
+ */
+ lib_ring_buffer_switch_old_end(buf, chan, &offsets, tsc);
+}
+EXPORT_SYMBOL_GPL(lib_ring_buffer_switch_slow);
+
+/*
+ * Returns :
+ * 0 if ok
+ * -ENOSPC if event size is too large for packet.
+ * -ENOBUFS if there is currently not enough space in buffer for the event.
+ * -EIO if data cannot be written into the buffer for any other reason.
+ */
+static
+int lib_ring_buffer_try_reserve_slow(struct lib_ring_buffer *buf,
+ struct channel *chan,
+ struct switch_offsets *offsets,
+ struct lib_ring_buffer_ctx *ctx)
+{
+ const struct lib_ring_buffer_config *config = chan->backend.config;
+ unsigned long reserve_commit_diff;
+
+ offsets->begin = v_read(config, &buf->offset);
+ offsets->old = offsets->begin;
+ offsets->switch_new_start = 0;
+ offsets->switch_new_end = 0;
+ offsets->switch_old_end = 0;
+ offsets->pre_header_padding = 0;
+
+ ctx->tsc = config->cb.ring_buffer_clock_read(chan);
+ if ((int64_t) ctx->tsc == -EIO)
+ return -EIO;
+
+ if (last_tsc_overflow(config, buf, ctx->tsc))
+ ctx->rflags |= RING_BUFFER_RFLAG_FULL_TSC;
+
+ if (unlikely(subbuf_offset(offsets->begin, ctx->chan) == 0)) {
+ offsets->switch_new_start = 1; /* For offsets->begin */
+ } else {
+ offsets->size = config->cb.record_header_size(config, chan,
+ offsets->begin,
+ &offsets->pre_header_padding,
+ ctx);
+ offsets->size +=
+ lib_ring_buffer_align(offsets->begin + offsets->size,
+ ctx->largest_align)
+ + ctx->data_size;
+ if (unlikely(subbuf_offset(offsets->begin, chan) +
+ offsets->size > chan->backend.subbuf_size)) {
+ offsets->switch_old_end = 1; /* For offsets->old */
+ offsets->switch_new_start = 1; /* For offsets->begin */
+ }
+ }
+ if (unlikely(offsets->switch_new_start)) {
+ unsigned long sb_index;
+
+ /*
+ * We are typically not filling the previous buffer completely.
+ */
+ if (likely(offsets->switch_old_end))
+ offsets->begin = subbuf_align(offsets->begin, chan);
+ offsets->begin = offsets->begin
+ + config->cb.subbuffer_header_size();
+ /* Test new buffer integrity */
+ sb_index = subbuf_index(offsets->begin, chan);
+ reserve_commit_diff =
+ (buf_trunc(offsets->begin, chan)
+ >> chan->backend.num_subbuf_order)
+ - ((unsigned long) v_read(config,
+ &buf->commit_cold[sb_index].cc_sb)
+ & chan->commit_count_mask);
+ if (likely(reserve_commit_diff == 0)) {
+ /* Next subbuffer not being written to. */
+ if (unlikely(config->mode != RING_BUFFER_OVERWRITE &&
+ subbuf_trunc(offsets->begin, chan)
+ - subbuf_trunc((unsigned long)
+ atomic_long_read(&buf->consumed), chan)
+ >= chan->backend.buf_size)) {
+ /*
+ * We do not overwrite non consumed buffers
+ * and we are full : record is lost.
+ */
+ v_inc(config, &buf->records_lost_full);
+ return -ENOBUFS;
+ } else {
+ /*
+ * Next subbuffer not being written to, and we
+ * are either in overwrite mode or the buffer is
+ * not full. It's safe to write in this new
+ * subbuffer.
+ */
+ }
+ } else {
+ /*
+ * Next subbuffer reserve offset does not match the
+ * commit offset. Drop record in producer-consumer and
+ * overwrite mode. Caused by either a writer OOPS or too
+ * many nested writes over a reserve/commit pair.
+ */
+ v_inc(config, &buf->records_lost_wrap);
+ return -EIO;
+ }
+ offsets->size =
+ config->cb.record_header_size(config, chan,
+ offsets->begin,
+ &offsets->pre_header_padding,
+ ctx);
+ offsets->size +=
+ lib_ring_buffer_align(offsets->begin + offsets->size,
+ ctx->largest_align)
+ + ctx->data_size;
+ if (unlikely(subbuf_offset(offsets->begin, chan)
+ + offsets->size > chan->backend.subbuf_size)) {
+ /*
+ * Record too big for subbuffers, report error, don't
+ * complete the sub-buffer switch.
+ */
+ v_inc(config, &buf->records_lost_big);
+ return -ENOSPC;
+ } else {
+ /*
+ * We just made a successful buffer switch and the
+ * record fits in the new subbuffer. Let's write.
+ */
+ }
+ } else {
+ /*
+ * Record fits in the current buffer and we are not on a switch
+ * boundary. It's safe to write.
+ */
+ }
+ offsets->end = offsets->begin + offsets->size;
+
+ if (unlikely(subbuf_offset(offsets->end, chan) == 0)) {
+ /*
+ * The offset_end will fall at the very beginning of the next
+ * subbuffer.
+ */
+ offsets->switch_new_end = 1; /* For offsets->begin */
+ }
+ return 0;
+}
+
+/**
+ * lib_ring_buffer_reserve_slow - Atomic slot reservation in a buffer.
+ * @ctx: ring buffer context.
+ *
+ * Return : -NOBUFS if not enough space, -ENOSPC if event size too large,
+ * -EIO for other errors, else returns 0.
+ * It will take care of sub-buffer switching.
+ */
+int lib_ring_buffer_reserve_slow(struct lib_ring_buffer_ctx *ctx)
+{
+ struct channel *chan = ctx->chan;
+ const struct lib_ring_buffer_config *config = chan->backend.config;
+ struct lib_ring_buffer *buf;
+ struct switch_offsets offsets;
+ int ret;
+
+ if (config->alloc == RING_BUFFER_ALLOC_PER_CPU)
+ buf = per_cpu_ptr(chan->backend.buf, ctx->cpu);
+ else
+ buf = chan->backend.buf;
+ ctx->buf = buf;
+
+ offsets.size = 0;
+
+ do {
+ ret = lib_ring_buffer_try_reserve_slow(buf, chan, &offsets,
+ ctx);
+ if (unlikely(ret))
+ return ret;
+ } while (unlikely(v_cmpxchg(config, &buf->offset, offsets.old,
+ offsets.end)
+ != offsets.old));
+
+ /*
+ * Atomically update last_tsc. This update races against concurrent
+ * atomic updates, but the race will always cause supplementary full TSC
+ * records, never the opposite (missing a full TSC record when it would
+ * be needed).
+ */
+ save_last_tsc(config, buf, ctx->tsc);
+
+ /*
+ * Push the reader if necessary
+ */
+ lib_ring_buffer_reserve_push_reader(buf, chan, offsets.end - 1);
+
+ /*
+ * Clear noref flag for this subbuffer.
+ */
+ lib_ring_buffer_clear_noref(config, &buf->backend,
+ subbuf_index(offsets.end - 1, chan));
+
+ /*
+ * Switch old subbuffer if needed.
+ */
+ if (unlikely(offsets.switch_old_end)) {
+ lib_ring_buffer_clear_noref(config, &buf->backend,
+ subbuf_index(offsets.old - 1, chan));
+ lib_ring_buffer_switch_old_end(buf, chan, &offsets, ctx->tsc);
+ }
+
+ /*
+ * Populate new subbuffer.
+ */
+ if (unlikely(offsets.switch_new_start))
+ lib_ring_buffer_switch_new_start(buf, chan, &offsets, ctx->tsc);
+
+ if (unlikely(offsets.switch_new_end))
+ lib_ring_buffer_switch_new_end(buf, chan, &offsets, ctx->tsc);
+
+ ctx->slot_size = offsets.size;
+ ctx->pre_offset = offsets.begin;
+ ctx->buf_offset = offsets.begin + offsets.pre_header_padding;
+ return 0;
+}
+EXPORT_SYMBOL_GPL(lib_ring_buffer_reserve_slow);