X-Git-Url: https://git.lttng.org/?a=blobdiff_plain;f=libringbuffer%2Ffrontend_internal.h;h=8a0f78f32ee774e19e853b3c7c511957ed7adb85;hb=3d1aec25c7cc70f4b240a4498d876d9782497cd4;hp=77a431295a71b495d72fff3de74c31b8aff761eb;hpb=34a91bdb42a2a3b01b687ab5e1ba7638401e6dfc;p=lttng-ust.git

diff --git a/libringbuffer/frontend_internal.h b/libringbuffer/frontend_internal.h
index 77a43129..8a0f78f3 100644
--- a/libringbuffer/frontend_internal.h
+++ b/libringbuffer/frontend_internal.h
@@ -365,6 +365,13 @@ void lib_ring_buffer_wakeup(struct lttng_ust_lib_ring_buffer *buf,
 	}
 }
 
+/*
+ * Receive end of subbuffer TSC as parameter. It has been read in the
+ * space reservation loop of either reserve or switch, which ensures it
+ * progresses monotonically with event records in the buffer. Therefore,
+ * it ensures that the end timestamp of a subbuffer is <= begin
+ * timestamp of the following subbuffers.
+ */
 static inline
 void lib_ring_buffer_check_deliver(const struct lttng_ust_lib_ring_buffer_config *config,
 				   struct lttng_ust_lib_ring_buffer *buf,
@@ -372,11 +379,11 @@ void lib_ring_buffer_check_deliver(const struct lttng_ust_lib_ring_buffer_config
 			           unsigned long offset,
 				   unsigned long commit_count,
 			           unsigned long idx,
-				   struct lttng_ust_shm_handle *handle)
+				   struct lttng_ust_shm_handle *handle,
+				   uint64_t tsc)
 {
 	unsigned long old_commit_count = commit_count
 					 - chan->backend.subbuf_size;
-	uint64_t tsc;
 
 	/* Check if all commits have been done */
 	if (caa_unlikely((buf_trunc(offset, chan) >> chan->backend.num_subbuf_order)
@@ -407,6 +414,12 @@ void lib_ring_buffer_check_deliver(const struct lttng_ust_lib_ring_buffer_config
 		 * The subbuffer size is least 2 bytes (minimum size: 1 page).
 		 * This guarantees that old_commit_count + 1 != commit_count.
 		 */
+
+		/*
+		 * Order prior updates to reserve count prior to the
+		 * commit_cold cc_sb update.
+		 */
+		cmm_smp_wmb();
 		if (caa_likely(v_cmpxchg(config, &shmp_index(handle, buf->commit_cold, idx)->cc_sb,
 					 old_commit_count, old_commit_count + 1)
 			   == old_commit_count)) {
@@ -416,7 +429,6 @@ void lib_ring_buffer_check_deliver(const struct lttng_ust_lib_ring_buffer_config
 			 * and any other writer trying to access this subbuffer
 			 * in this state is required to drop records.
 			 */
-			tsc = config->cb.ring_buffer_clock_read(chan);
 			v_add(config,
 			      subbuffer_get_records_count(config,
 							  &buf->backend,
@@ -452,6 +464,11 @@ void lib_ring_buffer_check_deliver(const struct lttng_ust_lib_ring_buffer_config
 			/* End of exclusive subbuffer access */
 			v_set(config, &shmp_index(handle, buf->commit_cold, idx)->cc_sb,
 			      commit_count);
+			/*
+			 * Order later updates to reserve count after
+			 * the commit cold cc_sb update.
+			 */
+			cmm_smp_wmb();
 			lib_ring_buffer_vmcore_check_deliver(config, buf,
 						 commit_count, idx, handle);