Merge tag 'trace-v5.14-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace

Pull tracing fixes from Steven Rostedt:

 - Fix deadloop in ring buffer because of using stale "read" variable

 - Fix synthetic event use of field_pos as boolean and not an index

 - Fixed histogram special var "cpu" overriding event fields called
   "cpu"

 - Cleaned up error prone logic in alloc_synth_event()

 - Removed call to synchronize_rcu_tasks_rude() when not needed

 - Removed redundant initialization of a local variable "ret"

 - Fixed kernel crash when updating tracepoint callbacks of different
   priorities.

* tag 'trace-v5.14-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace:
  tracepoints: Update static_call before tp_funcs when adding a tracepoint
  ftrace: Remove redundant initialization of variable ret
  ftrace: Avoid synchronize_rcu_tasks_rude() call when not necessary
  tracing: Clean up alloc_synth_event()
  tracing/histogram: Rename "cpu" to "common_cpu"
  tracing: Synthetic event field_pos is an index not a boolean
  tracing: Fix bug in rb_per_cpu_empty() that might cause deadloop.

1 files changed, 24 insertions, 4 deletions

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index d1463eac11a3..e592d1df6f88 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -3880,10 +3880,30 @@ static bool rb_per_cpu_empty(struct ring_buffer_per_cpu *cpu_buffer)
 	if (unlikely(!head))
 		return true;
 
-	return reader->read == rb_page_commit(reader) &&
-		(commit == reader ||
-		 (commit == head &&
-		  head->read == rb_page_commit(commit)));
+	/* Reader should exhaust content in reader page */
+	if (reader->read != rb_page_commit(reader))
+		return false;
+
+	/*
+	 * If writers are committing on the reader page, knowing all
+	 * committed content has been read, the ring buffer is empty.
+	 */
+	if (commit == reader)
+		return true;
+
+	/*
+	 * If writers are committing on a page other than reader page
+	 * and head page, there should always be content to read.
+	 */
+	if (commit != head)
+		return false;
+
+	/*
+	 * Writers are committing on the head page, we just need
+	 * to care about there're committed data, and the reader will
+	 * swap reader page with head page when it is to read data.
+	 */
+	return rb_page_commit(commit) == 0;
 }
 
 /**