* 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.
}
/*
- * 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)
{
}
}
-/*
- * Called with ust_lock() held.
- */
static
void lib_ring_buffer_channel_switch_timer_stop(struct channel *chan)
{
- sigset_t pending_set;
int ret;
if (!chan->switch_timer_interval || !chan->switch_timer_enabled)
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");
- }
- if (!sigismember(&pending_set, LTTNG_UST_RB_SIG_FLUSH))
- 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;
}
-/*
- * Called with ust_lock() held.
- */
static
void lib_ring_buffer_channel_read_timer_start(struct channel *chan)
{
}
}
-/*
- * Called with ust_lock() held.
- */
static
void lib_ring_buffer_channel_read_timer_stop(struct channel *chan)
{
const struct lttng_ust_lib_ring_buffer_config *config = &chan->backend.config;
- sigset_t pending_set;
int ret;
if (config->wakeup != RING_BUFFER_WAKEUP_BY_TIMER
*/
lib_ring_buffer_channel_do_read(chan);
-
- /*
- * 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, LTTNG_UST_RB_SIG_READ))
- 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_READ);
chan->read_timer = 0;
chan->read_timer_enabled = 0;
*/
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;
* 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;
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(),
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);
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(),
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);
+ commit_count, endidx, handle, tsc);
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