X-Git-Url: http://git.liburcu.org/?a=blobdiff_plain;f=libringbuffer%2Ffrontend_internal.h;h=f6d91bde2bf63f0917b9bd27b90e73ed54429bcc;hb=fb31eb73d8a4a6d9784ed5c335b7fa3b9684108c;hp=10d6c4db789bbf498e3188a1a339c5e94223653f;hpb=d2fe4771f15b6e50969bea1d7fcd74edca307de3;p=lttng-ust.git

diff --git a/libringbuffer/frontend_internal.h b/libringbuffer/frontend_internal.h
index 10d6c4db..f6d91bde 100644
--- a/libringbuffer/frontend_internal.h
+++ b/libringbuffer/frontend_internal.h
@@ -34,6 +34,7 @@
 #include <urcu/compiler.h>
 #include <urcu/tls-compat.h>
 #include <signal.h>
+#include <stdint.h>
 #include <pthread.h>
 
 #include <lttng/ringbuffer-config.h>
@@ -158,7 +159,8 @@ int last_tsc_overflow(const struct lttng_ust_lib_ring_buffer_config *config,
 #endif
 
 extern
-int lib_ring_buffer_reserve_slow(struct lttng_ust_lib_ring_buffer_ctx *ctx);
+int lib_ring_buffer_reserve_slow(struct lttng_ust_lib_ring_buffer_ctx *ctx,
+		void *client_ctx);
 
 extern
 void lib_ring_buffer_switch_slow(struct lttng_ust_lib_ring_buffer *buf,
@@ -204,6 +206,39 @@ void lib_ring_buffer_reserve_push_reader(struct lttng_ust_lib_ring_buffer *buf,
 					      consumed_new) != consumed_old));
 }
 
+/*
+ * Move consumed position to the beginning of subbuffer in which the
+ * write offset is. Should only be used on ring buffers that are not
+ * actively being written into, because clear_reader does not take into
+ * account the commit counters when moving the consumed position, which
+ * can make concurrent trace producers or consumers observe consumed
+ * position further than the write offset, which breaks ring buffer
+ * algorithm guarantees.
+ */
+static inline
+void lib_ring_buffer_clear_reader(struct lttng_ust_lib_ring_buffer *buf,
+				  struct lttng_ust_shm_handle *handle)
+{
+	struct channel *chan;
+	const struct lttng_ust_lib_ring_buffer_config *config;
+	unsigned long offset, consumed_old, consumed_new;
+
+	chan = shmp(handle, buf->backend.chan);
+	if (!chan)
+		return;
+	config = &chan->backend.config;
+
+	do {
+		offset = v_read(config, &buf->offset);
+		consumed_old = uatomic_read(&buf->consumed);
+		CHAN_WARN_ON(chan, (long) (subbuf_trunc(offset, chan)
+				- subbuf_trunc(consumed_old, chan))
+				< 0);
+		consumed_new = subbuf_trunc(offset, chan);
+	} while (caa_unlikely(uatomic_cmpxchg(&buf->consumed, consumed_old,
+					      consumed_new) != consumed_old));
+}
+
 static inline
 int lib_ring_buffer_pending_data(const struct lttng_ust_lib_ring_buffer_config *config,
 				 struct lttng_ust_lib_ring_buffer *buf,
@@ -233,6 +268,7 @@ int lib_ring_buffer_reserve_committed(const struct lttng_ust_lib_ring_buffer_con
 				      struct lttng_ust_shm_handle *handle)
 {
 	unsigned long offset, idx, commit_count;
+	struct commit_counters_hot *cc_hot;
 
 	CHAN_WARN_ON(chan, config->alloc != RING_BUFFER_ALLOC_PER_CPU);
 	CHAN_WARN_ON(chan, config->sync != RING_BUFFER_SYNC_PER_CPU);
@@ -248,7 +284,10 @@ int lib_ring_buffer_reserve_committed(const struct lttng_ust_lib_ring_buffer_con
 	do {
 		offset = v_read(config, &buf->offset);
 		idx = subbuf_index(offset, chan);
-		commit_count = v_read(config, &shmp_index(handle, buf->commit_hot, idx)->cc);
+		cc_hot = shmp_index(handle, buf->commit_hot, idx);
+		if (caa_unlikely(!cc_hot))
+			return 0;
+		commit_count = v_read(config, &cc_hot->cc);
 	} while (offset != v_read(config, &buf->offset));
 
 	return ((buf_trunc(offset, chan) >> chan->backend.num_subbuf_order)