#include <urcu/compiler.h>
#include <urcu/ref.h>
#include <urcu/tls-compat.h>
+#include <poll.h>
#include <helper.h>
#include "smp.h"
/* Print DBG() messages about events lost only every 1048576 hits */
#define DBG_PRINT_NR_LOST (1UL << 20)
-#define LTTNG_UST_RB_SIG SIGRTMIN
-#define LTTNG_UST_RB_SIG_TEARDOWN SIGRTMIN + 1
+#define LTTNG_UST_RB_SIG_FLUSH SIGRTMIN
+#define LTTNG_UST_RB_SIG_READ SIGRTMIN + 1
+#define LTTNG_UST_RB_SIG_TEARDOWN SIGRTMIN + 2
#define CLOCKID CLOCK_MONOTONIC
+#define LTTNG_UST_RING_BUFFER_GET_RETRY 10
+#define LTTNG_UST_RING_BUFFER_RETRY_DELAY_MS 10
/*
* Use POSIX SHM: shm_open(3) and shm_unlink(3).
* Handle timer teardown race wrt memory free of private data by
* ring buffer signals are handled by a single thread, which permits
* a synchronization point between handling of each signal.
- * Protected by the ust mutex.
+ * Protected by the lock within the structure.
*/
struct timer_signal_data {
pthread_t tid; /* thread id managing signals */
int setup_done;
int qs_done;
+ pthread_mutex_t lock;
};
-static struct timer_signal_data timer_signal;
+static struct timer_signal_data timer_signal = {
+ .tid = 0,
+ .setup_done = 0,
+ .qs_done = 0,
+ .lock = PTHREAD_MUTEX_INITIALIZER,
+};
/**
* lib_ring_buffer_reset - Reset ring buffer to initial values.
handle = chan->handle;
config = &chan->backend.config;
- DBG("Timer for channel %p\n", chan);
+ DBG("Switch timer for channel %p\n", chan);
/*
* Only flush buffers periodically if readers are active.
struct lttng_ust_lib_ring_buffer *buf =
shmp(handle, chan->backend.buf[0].shmp);
- if (uatomic_read(&buf->active_readers))
- lib_ring_buffer_switch_slow(buf, SWITCH_ACTIVE,
- chan->handle);
+ if (uatomic_read(&buf->active_readers))
+ lib_ring_buffer_switch_slow(buf, SWITCH_ACTIVE,
+ chan->handle);
}
pthread_mutex_unlock(&wakeup_fd_mutex);
return;
}
+static
+void lib_ring_buffer_channel_do_read(struct channel *chan)
+{
+ const struct lttng_ust_lib_ring_buffer_config *config;
+ struct lttng_ust_shm_handle *handle;
+ int cpu;
+
+ handle = chan->handle;
+ config = &chan->backend.config;
+
+ /*
+ * Only flush buffers periodically if readers are active.
+ */
+ pthread_mutex_lock(&wakeup_fd_mutex);
+ if (config->alloc == RING_BUFFER_ALLOC_PER_CPU) {
+ for_each_possible_cpu(cpu) {
+ struct lttng_ust_lib_ring_buffer *buf =
+ shmp(handle, chan->backend.buf[cpu].shmp);
+
+ if (uatomic_read(&buf->active_readers)
+ && lib_ring_buffer_poll_deliver(config, buf,
+ chan, handle)) {
+ lib_ring_buffer_wakeup(buf, handle);
+ }
+ }
+ } else {
+ struct lttng_ust_lib_ring_buffer *buf =
+ shmp(handle, chan->backend.buf[0].shmp);
+
+ if (uatomic_read(&buf->active_readers)
+ && lib_ring_buffer_poll_deliver(config, buf,
+ chan, handle)) {
+ lib_ring_buffer_wakeup(buf, handle);
+ }
+ }
+ pthread_mutex_unlock(&wakeup_fd_mutex);
+}
+
+static
+void lib_ring_buffer_channel_read_timer(int sig, siginfo_t *si, void *uc)
+{
+ struct channel *chan;
+
+ assert(CMM_LOAD_SHARED(timer_signal.tid) == pthread_self());
+ chan = si->si_value.sival_ptr;
+ DBG("Read timer for channel %p\n", chan);
+ lib_ring_buffer_channel_do_read(chan);
+ return;
+}
+
static
void rb_setmask(sigset_t *mask)
{
if (ret) {
PERROR("sigemptyset");
}
- ret = sigaddset(mask, LTTNG_UST_RB_SIG);
+ ret = sigaddset(mask, LTTNG_UST_RB_SIG_FLUSH);
+ if (ret) {
+ PERROR("sigaddset");
+ }
+ ret = sigaddset(mask, LTTNG_UST_RB_SIG_READ);
if (ret) {
PERROR("sigaddset");
}
for (;;) {
signr = sigwaitinfo(&mask, &info);
if (signr == -1) {
- PERROR("sigwaitinfo");
+ if (errno != EINTR)
+ PERROR("sigwaitinfo");
continue;
}
- if (signr == LTTNG_UST_RB_SIG) {
+ if (signr == LTTNG_UST_RB_SIG_FLUSH) {
lib_ring_buffer_channel_switch_timer(info.si_signo,
&info, NULL);
+ } else if (signr == LTTNG_UST_RB_SIG_READ) {
+ lib_ring_buffer_channel_read_timer(info.si_signo,
+ &info, NULL);
} else if (signr == LTTNG_UST_RB_SIG_TEARDOWN) {
cmm_smp_mb();
CMM_STORE_SHARED(timer_signal.qs_done, 1);
}
/*
- * Called with ust_lock() held.
* Ensure only a single thread listens on the timer signal.
*/
static
pthread_t thread;
int ret;
+ pthread_mutex_lock(&timer_signal.lock);
if (timer_signal.setup_done)
- return;
+ goto end;
ret = pthread_create(&thread, NULL, &sig_thread, NULL);
if (ret) {
PERROR("pthread_detach");
}
timer_signal.setup_done = 1;
+end:
+ pthread_mutex_unlock(&timer_signal.lock);
}
/*
- * Called with ust_lock() held.
+ * Wait for signal-handling thread quiescent state.
*/
+static
+void lib_ring_buffer_wait_signal_thread_qs(unsigned int signr)
+{
+ sigset_t pending_set;
+ int ret;
+
+ /*
+ * We need to be the only thread interacting with the thread
+ * that manages signals for teardown synchronization.
+ */
+ pthread_mutex_lock(&timer_signal.lock);
+
+ /*
+ * Ensure we don't have any signal queued for this channel.
+ */
+ for (;;) {
+ ret = sigemptyset(&pending_set);
+ if (ret == -1) {
+ PERROR("sigemptyset");
+ }
+ ret = sigpending(&pending_set);
+ if (ret == -1) {
+ PERROR("sigpending");
+ }
+ if (!sigismember(&pending_set, signr))
+ break;
+ caa_cpu_relax();
+ }
+
+ /*
+ * From this point, no new signal handler will be fired that
+ * would try to access "chan". However, we still need to wait
+ * for any currently executing handler to complete.
+ */
+ cmm_smp_mb();
+ CMM_STORE_SHARED(timer_signal.qs_done, 0);
+ cmm_smp_mb();
+
+ /*
+ * Kill with LTTNG_UST_RB_SIG_TEARDOWN, so signal management
+ * thread wakes up.
+ */
+ kill(getpid(), LTTNG_UST_RB_SIG_TEARDOWN);
+
+ while (!CMM_LOAD_SHARED(timer_signal.qs_done))
+ caa_cpu_relax();
+ cmm_smp_mb();
+
+ pthread_mutex_unlock(&timer_signal.lock);
+}
+
static
void lib_ring_buffer_channel_switch_timer_start(struct channel *chan)
{
lib_ring_buffer_setup_timer_thread();
sev.sigev_notify = SIGEV_SIGNAL;
- sev.sigev_signo = LTTNG_UST_RB_SIG;
+ sev.sigev_signo = LTTNG_UST_RB_SIG_FLUSH;
sev.sigev_value.sival_ptr = chan;
ret = timer_create(CLOCKID, &sev, &chan->switch_timer);
if (ret == -1) {
}
}
-/*
- * Called with ust_lock() held.
- */
static
void lib_ring_buffer_channel_switch_timer_stop(struct channel *chan)
{
- sigset_t pending_set;
- int sig_is_pending, ret;
+ int ret;
if (!chan->switch_timer_interval || !chan->switch_timer_enabled)
return;
PERROR("timer_delete");
}
- /*
- * Ensure we don't have any signal queued for this channel.
- */
- for (;;) {
- ret = sigemptyset(&pending_set);
- if (ret == -1) {
- PERROR("sigemptyset");
- }
- ret = sigpending(&pending_set);
- if (ret == -1) {
- PERROR("sigpending");
- }
- sig_is_pending = sigismember(&pending_set, LTTNG_UST_RB_SIG);
- if (!sig_is_pending)
- break;
- caa_cpu_relax();
- }
-
- /*
- * From this point, no new signal handler will be fired that
- * would try to access "chan". However, we still need to wait
- * for any currently executing handler to complete.
- */
- cmm_smp_mb();
- CMM_STORE_SHARED(timer_signal.qs_done, 0);
- cmm_smp_mb();
-
- /*
- * Kill with LTTNG_UST_RB_SIG_TEARDOWN, so signal management
- * thread wakes up.
- */
- kill(getpid(), LTTNG_UST_RB_SIG_TEARDOWN);
-
- while (!CMM_LOAD_SHARED(timer_signal.qs_done))
- caa_cpu_relax();
- cmm_smp_mb();
+ lib_ring_buffer_wait_signal_thread_qs(LTTNG_UST_RB_SIG_FLUSH);
chan->switch_timer = 0;
chan->switch_timer_enabled = 0;
}
-#if 0
-/*
- * Polling timer to check the channels for data.
- */
-static void read_buffer_timer(unsigned long data)
+static
+void lib_ring_buffer_channel_read_timer_start(struct channel *chan)
{
- struct lttng_ust_lib_ring_buffer *buf = (struct lttng_ust_lib_ring_buffer *)data;
- struct channel *chan = shmp(handle, buf->backend.chan);
const struct lttng_ust_lib_ring_buffer_config *config = &chan->backend.config;
+ struct sigevent sev;
+ struct itimerspec its;
+ int ret;
- CHAN_WARN_ON(chan, !buf->backend.allocated);
+ if (config->wakeup != RING_BUFFER_WAKEUP_BY_TIMER
+ || !chan->read_timer_interval || chan->read_timer_enabled)
+ return;
- if (uatomic_read(&buf->active_readers))
- && lib_ring_buffer_poll_deliver(config, buf, chan)) {
- //TODO
- //wake_up_interruptible(&buf->read_wait);
- //wake_up_interruptible(&chan->read_wait);
- }
+ chan->read_timer_enabled = 1;
- //TODO
- //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);
-}
-#endif //0
+ lib_ring_buffer_setup_timer_thread();
-static void lib_ring_buffer_start_read_timer(struct lttng_ust_lib_ring_buffer *buf,
- struct lttng_ust_shm_handle *handle)
-{
- struct channel *chan = shmp(handle, buf->backend.chan);
- const struct lttng_ust_lib_ring_buffer_config *config = &chan->backend.config;
+ sev.sigev_notify = SIGEV_SIGNAL;
+ sev.sigev_signo = LTTNG_UST_RB_SIG_READ;
+ sev.sigev_value.sival_ptr = chan;
+ ret = timer_create(CLOCKID, &sev, &chan->read_timer);
+ if (ret == -1) {
+ PERROR("timer_create");
+ }
- if (config->wakeup != RING_BUFFER_WAKEUP_BY_TIMER
- || !chan->read_timer_interval
- || buf->read_timer_enabled)
- return;
+ its.it_value.tv_sec = chan->read_timer_interval / 1000000;
+ its.it_value.tv_nsec = chan->read_timer_interval % 1000000;
+ its.it_interval.tv_sec = its.it_value.tv_sec;
+ its.it_interval.tv_nsec = its.it_value.tv_nsec;
- //TODO
- //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;
+ ret = timer_settime(chan->read_timer, 0, &its, NULL);
+ if (ret == -1) {
+ PERROR("timer_settime");
+ }
}
-static void lib_ring_buffer_stop_read_timer(struct lttng_ust_lib_ring_buffer *buf,
- struct lttng_ust_shm_handle *handle)
+static
+void lib_ring_buffer_channel_read_timer_stop(struct channel *chan)
{
- struct channel *chan = shmp(handle, buf->backend.chan);
const struct lttng_ust_lib_ring_buffer_config *config = &chan->backend.config;
+ int ret;
if (config->wakeup != RING_BUFFER_WAKEUP_BY_TIMER
- || !chan->read_timer_interval
- || !buf->read_timer_enabled)
+ || !chan->read_timer_interval || !chan->read_timer_enabled)
return;
- //TODO
- //del_timer_sync(&buf->read_timer);
+ ret = timer_delete(chan->read_timer);
+ if (ret == -1) {
+ PERROR("timer_delete");
+ }
+
/*
* 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, handle)) {
- //TODO
- //wake_up_interruptible(&buf->read_wait);
- //wake_up_interruptible(&chan->read_wait);
- }
- buf->read_timer_enabled = 0;
+ lib_ring_buffer_channel_do_read(chan);
+
+ lib_ring_buffer_wait_signal_thread_qs(LTTNG_UST_RB_SIG_READ);
+
+ chan->read_timer = 0;
+ chan->read_timer_enabled = 0;
}
static void channel_unregister_notifiers(struct channel *chan,
struct lttng_ust_shm_handle *handle)
{
- const struct lttng_ust_lib_ring_buffer_config *config = &chan->backend.config;
- int cpu;
-
lib_ring_buffer_channel_switch_timer_stop(chan);
- if (config->alloc == RING_BUFFER_ALLOC_PER_CPU) {
- for_each_possible_cpu(cpu) {
- struct lttng_ust_lib_ring_buffer *buf = shmp(handle, chan->backend.buf[cpu].shmp);
-
- lib_ring_buffer_stop_read_timer(buf, handle);
- }
- } else {
- struct lttng_ust_lib_ring_buffer *buf = shmp(handle, chan->backend.buf[0].shmp);
-
- lib_ring_buffer_stop_read_timer(buf, handle);
- }
- //channel_backend_unregister_notifiers(&chan->backend);
+ lib_ring_buffer_channel_read_timer_stop(chan);
}
static void channel_print_errors(struct channel *chan,
size_t num_subbuf, unsigned int switch_timer_interval,
unsigned int read_timer_interval)
{
- int ret, cpu;
+ int ret;
size_t shmsize, chansize;
struct channel *chan;
struct lttng_ust_shm_handle *handle;
chan->handle = handle;
chan->commit_count_mask = (~0UL >> chan->backend.num_subbuf_order);
- chan->switch_timer_interval = switch_timer_interval;
-
- //TODO
- //chan->read_timer_interval = read_timer_interval;
- //init_waitqueue_head(&chan->read_wait);
- //init_waitqueue_head(&chan->hp_wait);
+ chan->switch_timer_interval = switch_timer_interval;
+ chan->read_timer_interval = read_timer_interval;
lib_ring_buffer_channel_switch_timer_start(chan);
- if (config->alloc == RING_BUFFER_ALLOC_PER_CPU) {
- /*
- * 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.
- */
- for_each_possible_cpu(cpu) {
- struct lttng_ust_lib_ring_buffer *buf = shmp(handle, chan->backend.buf[cpu].shmp);
- lib_ring_buffer_start_read_timer(buf, handle);
- }
- } else {
- struct lttng_ust_lib_ring_buffer *buf = shmp(handle, chan->backend.buf[0].shmp);
+ lib_ring_buffer_channel_read_timer_start(chan);
- lib_ring_buffer_start_read_timer(buf, handle);
- }
return handle;
error_backend_init:
}
/**
- * lib_ring_buffer_put_snapshot - move consumed counter forward
+ * lib_ring_buffer_move_consumer - move consumed counter forward
* @buf: ring buffer
* @consumed_new: new consumed count value
*/
struct channel *chan = shmp(handle, buf->backend.chan);
const struct lttng_ust_lib_ring_buffer_config *config = &chan->backend.config;
unsigned long consumed_cur, consumed_idx, commit_count, write_offset;
- int ret;
- int finalized;
+ int ret, finalized, nr_retry = LTTNG_UST_RING_BUFFER_GET_RETRY;
retry:
finalized = CMM_ACCESS_ONCE(buf->finalized);
/*
* Check that the subbuffer we are trying to consume has been
- * already fully committed.
+ * already fully committed. There are a few causes that can make
+ * this unavailability situation occur:
+ *
+ * Temporary (short-term) situation:
+ * - Application is running on a different CPU, between reserve
+ * and commit ring buffer operations,
+ * - Application is preempted between reserve and commit ring
+ * buffer operations,
+ *
+ * Long-term situation:
+ * - Application is stopped (SIGSTOP) between reserve and commit
+ * ring buffer operations. Could eventually be resumed by
+ * SIGCONT.
+ * - Application is killed (SIGTERM, SIGINT, SIGKILL) between
+ * reserve and commit ring buffer operation.
+ *
+ * From a consumer perspective, handling short-term
+ * unavailability situations is performed by retrying a few
+ * times after a delay. Handling long-term unavailability
+ * situations is handled by failing to get the sub-buffer.
+ *
+ * In all of those situations, if the application is taking a
+ * long time to perform its commit after ring buffer space
+ * reservation, we can end up in a situation where the producer
+ * will fill the ring buffer and try to write into the same
+ * sub-buffer again (which has a missing commit). This is
+ * handled by the producer in the sub-buffer switch handling
+ * code of the reserve routine by detecting unbalanced
+ * reserve/commit counters and discarding all further events
+ * until the situation is resolved in those situations. Two
+ * scenarios can occur:
+ *
+ * 1) The application causing the reserve/commit counters to be
+ * unbalanced has been terminated. In this situation, all
+ * further events will be discarded in the buffers, and no
+ * further buffer data will be readable by the consumer
+ * daemon. Tearing down the UST tracing session and starting
+ * anew is a work-around for those situations. Note that this
+ * only affects per-UID tracing. In per-PID tracing, the
+ * application vanishes with the termination, and therefore
+ * no more data needs to be written to the buffers.
+ * 2) The application causing the unbalance has been delayed for
+ * a long time, but will eventually try to increment the
+ * commit counter after eventually writing to the sub-buffer.
+ * This situation can cause events to be discarded until the
+ * application resumes its operations.
*/
if (((commit_count - chan->backend.subbuf_size)
& chan->commit_count_mask)
- - (buf_trunc(consumed_cur, chan)
+ - (buf_trunc(consumed, chan)
>> chan->backend.num_subbuf_order)
- != 0)
- goto nodata;
+ != 0) {
+ if (nr_retry-- > 0) {
+ if (nr_retry <= (LTTNG_UST_RING_BUFFER_GET_RETRY >> 1))
+ (void) poll(NULL, 0, LTTNG_UST_RING_BUFFER_RETRY_DELAY_MS);
+ goto retry;
+ } else {
+ 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)
+ if (subbuf_trunc(write_offset, chan) - subbuf_trunc(consumed, chan)
== 0)
goto nodata;
* 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.
+ *
+ * The short-lived race window described here can be affected by
+ * application signals and preemption, thus requiring to bound
+ * the loop to a maximum number of retry.
*/
ret = update_read_sb_index(config, &buf->backend, &chan->backend,
consumed_idx, buf_trunc_val(consumed, chan),
handle);
- if (ret)
- goto retry;
+ if (ret) {
+ if (nr_retry-- > 0) {
+ if (nr_retry <= (LTTNG_UST_RING_BUFFER_GET_RETRY >> 1))
+ (void) poll(NULL, 0, LTTNG_UST_RING_BUFFER_RETRY_DELAY_MS);
+ goto retry;
+ } else {
+ goto nodata;
+ }
+ }
subbuffer_id_clear_noref(config, &buf->backend.buf_rsb.id);
buf->get_subbuf_consumed = consumed;
commit_count = v_read(config, &shmp_index(handle, 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, handle);
+ commit_count, oldidx, handle, tsc);
lib_ring_buffer_write_commit_counter(config, buf, chan, oldidx,
- offsets->old, commit_count,
- config->cb.subbuffer_header_size(),
- handle);
+ offsets->old + config->cb.subbuffer_header_size(),
+ commit_count, handle);
}
/*
v_add(config, padding_size, &shmp_index(handle, buf->commit_hot, oldidx)->cc);
commit_count = v_read(config, &shmp_index(handle, buf->commit_hot, oldidx)->cc);
lib_ring_buffer_check_deliver(config, buf, chan, offsets->old - 1,
- commit_count, oldidx, handle);
+ commit_count, oldidx, handle, tsc);
lib_ring_buffer_write_commit_counter(config, buf, chan, oldidx,
- offsets->old, commit_count,
- padding_size, handle);
+ offsets->old + padding_size, commit_count, handle);
}
/*
commit_count = v_read(config, &shmp_index(handle, 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, handle);
+ commit_count, beginidx, handle, tsc);
lib_ring_buffer_write_commit_counter(config, buf, chan, beginidx,
- offsets->begin, commit_count,
- config->cb.subbuffer_header_size(),
- handle);
+ offsets->begin + config->cb.subbuffer_header_size(),
+ commit_count, handle);
}
/*
* 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.
+ * Calls subbuffer_set_data_size() to set the data size of the current
+ * sub-buffer. We do not need to perform check_deliver nor commit here,
+ * since this task will be done by the "commit" of the event for which
+ * we are currently doing the space reservation.
*/
static
void lib_ring_buffer_switch_new_end(struct lttng_ust_lib_ring_buffer *buf,
struct lttng_ust_shm_handle *handle)
{
const struct lttng_ust_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;
+ unsigned long endidx, data_size;
+ endidx = subbuf_index(offsets->end - 1, chan);
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,
handle);
-
- /*
- * Order all writes to buffer before the commit count update that will
- * determine that the subbuffer is full.
- */
- cmm_smp_wmb();
- v_add(config, padding_size, &shmp_index(handle, buf->commit_hot, endidx)->cc);
- commit_count = v_read(config, &shmp_index(handle, buf->commit_hot, endidx)->cc);
- lib_ring_buffer_check_deliver(config, buf, chan, offsets->end - 1,
- commit_count, endidx, handle);
- lib_ring_buffer_write_commit_counter(config, buf, chan, endidx,
- offsets->end, commit_count,
- padding_size, handle);
}
/*
struct lttng_ust_lib_ring_buffer *buf,
struct channel *chan,
struct switch_offsets *offsets,
- uint64_t *tsc)
+ uint64_t *tsc,
+ struct lttng_ust_shm_handle *handle)
{
const struct lttng_ust_lib_ring_buffer_config *config = &chan->backend.config;
- unsigned long off;
+ unsigned long off, reserve_commit_diff;
offsets->begin = v_read(config, &buf->offset);
offsets->old = offsets->begin;
* timestamps) are visible to the reader. This is required for
* quiescence guarantees for the fusion merge.
*/
- if (mode == SWITCH_FLUSH || off > 0) {
- if (caa_unlikely(off == 0)) {
- /*
- * A final flush that encounters an empty
- * sub-buffer cannot switch buffer if a
- * reader is located within this sub-buffer.
- * Anyway, the purpose of final flushing of a
- * sub-buffer at offset 0 is to handle the case
- * of entirely empty stream.
- */
- if (caa_unlikely(subbuf_trunc(offsets->begin, chan)
- - subbuf_trunc((unsigned long)
- uatomic_read(&buf->consumed), chan)
- >= chan->backend.buf_size))
- return -1;
- /*
- * 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())
+ if (mode != SWITCH_FLUSH && !off)
+ return -1; /* we do not have to switch : buffer is empty */
+
+ if (caa_unlikely(off == 0)) {
+ unsigned long sb_index, commit_count;
+
+ /*
+ * We are performing a SWITCH_FLUSH. At this stage, there are no
+ * concurrent writes into the buffer.
+ *
+ * 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;
+
+ /* Test new buffer integrity */
+ sb_index = subbuf_index(offsets->begin, chan);
+ commit_count = v_read(config,
+ &shmp_index(handle, buf->commit_cold,
+ sb_index)->cc_sb);
+ reserve_commit_diff =
+ (buf_trunc(offsets->begin, chan)
+ >> chan->backend.num_subbuf_order)
+ - (commit_count & chan->commit_count_mask);
+ if (caa_likely(reserve_commit_diff == 0)) {
+ /* Next subbuffer not being written to. */
+ if (caa_unlikely(config->mode != RING_BUFFER_OVERWRITE &&
+ subbuf_trunc(offsets->begin, chan)
+ - subbuf_trunc((unsigned long)
+ uatomic_read(&buf->consumed), chan)
+ >= chan->backend.buf_size)) {
+ /*
+ * We do not overwrite non consumed buffers
+ * and we are full : don't switch.
+ */
return -1;
+ } 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 {
/*
- * Need to write the subbuffer start header on finalize.
+ * Next subbuffer reserve offset does not match the
+ * commit offset. Don't perform switch in
+ * producer-consumer and overwrite mode. Caused by
+ * either a writer OOPS or too many nested writes over a
+ * reserve/commit pair.
*/
- offsets->switch_old_start = 1;
+ return -1;
}
- offsets->begin = subbuf_align(offsets->begin, chan);
- } else
- return -1; /* we do not have to switch : buffer is empty */
+
+ /*
+ * Need to write the subbuffer start header on finalize.
+ */
+ offsets->switch_old_start = 1;
+ }
+ offsets->begin = subbuf_align(offsets->begin, chan);
/* Note: old points to the next subbuf at offset 0 */
offsets->end = offsets->begin;
return 0;
*/
do {
if (lib_ring_buffer_try_switch_slow(mode, buf, chan, &offsets,
- &tsc))
+ &tsc, handle))
return; /* Switch not needed */
} while (v_cmpxchg(config, &buf->offset, offsets.old, offsets.end)
!= offsets.old);
{
const struct lttng_ust_lib_ring_buffer_config *config = &chan->backend.config;
struct lttng_ust_shm_handle *handle = ctx->handle;
- unsigned long reserve_commit_diff;
+ unsigned long reserve_commit_diff, offset_cmp;
- offsets->begin = v_read(config, &buf->offset);
+retry:
+ offsets->begin = offset_cmp = v_read(config, &buf->offset);
offsets->old = offsets->begin;
offsets->switch_new_start = 0;
offsets->switch_new_end = 0;
}
}
if (caa_unlikely(offsets->switch_new_start)) {
- unsigned long sb_index;
+ unsigned long sb_index, commit_count;
/*
* We are typically not filling the previous buffer completely.
+ config->cb.subbuffer_header_size();
/* Test new buffer integrity */
sb_index = subbuf_index(offsets->begin, chan);
+ /*
+ * Read buf->offset before buf->commit_cold[sb_index].cc_sb.
+ * lib_ring_buffer_check_deliver() has the matching
+ * memory barriers required around commit_cold cc_sb
+ * updates to ensure reserve and commit counter updates
+ * are not seen reordered when updated by another CPU.
+ */
+ cmm_smp_rmb();
+ commit_count = v_read(config,
+ &shmp_index(handle, buf->commit_cold,
+ sb_index)->cc_sb);
+ /* Read buf->commit_cold[sb_index].cc_sb before buf->offset. */
+ cmm_smp_rmb();
+ if (caa_unlikely(offset_cmp != v_read(config, &buf->offset))) {
+ /*
+ * The reserve counter have been concurrently updated
+ * while we read the commit counter. This means the
+ * commit counter we read might not match buf->offset
+ * due to concurrent update. We therefore need to retry.
+ */
+ goto retry;
+ }
reserve_commit_diff =
(buf_trunc(offsets->begin, chan)
>> chan->backend.num_subbuf_order)
- - ((unsigned long) v_read(config,
- &shmp_index(handle, buf->commit_cold, sb_index)->cc_sb)
- & chan->commit_count_mask);
+ - (commit_count & chan->commit_count_mask);
if (caa_likely(reserve_commit_diff == 0)) {
/* Next subbuffer not being written to. */
if (caa_unlikely(config->mode != RING_BUFFER_OVERWRITE &&
/*
* Next subbuffer reserve offset does not match the
- * commit offset. Drop record in producer-consumer and
+ * commit offset, and this did not involve update to the
+ * reserve counter. Drop record in producer-consumer and
* overwrite mode. Caused by either a writer OOPS or too
* many nested writes over a reserve/commit pair.
*/
projects / lttng-ust.git / blobdiff