Fix stack trace entry size to stop showing garbage

The macro that creates both the structure and the format displayed
 to user space for the stack trace event was changed a while ago
 to fix the parsing by user space tooling. But this change also modified
 the structure used to store the stack trace event. It changed the
 caller array field from [0] to [8]. Even though the size in the ring
 buffer is dynamic and can be something other than 8 (user space knows
 how to handle this), the 8 extra words was not accounted for when
 reserving the event on the ring buffer, and added 8 more entries, due
 to the calculation of "sizeof(*entry) + nr_entries * sizeof(long)",
 as the sizeof(*entry) now contains 8 entries. The size of the caller
 field needs to be subtracted from the size of the entry to create
 the correct allocation size.
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Merge tag 'trace-v5.12-rc5-2' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace

Pull tracing fix from Steven Rostedt:
 "Fix stack trace entry size to stop showing garbage

  The macro that creates both the structure and the format displayed to
  user space for the stack trace event was changed a while ago to fix
  the parsing by user space tooling. But this change also modified the
  structure used to store the stack trace event. It changed the caller
  array field from [0] to [8].

  Even though the size in the ring buffer is dynamic and can be
  something other than 8 (user space knows how to handle this), the 8
  extra words was not accounted for when reserving the event on the ring
  buffer, and added 8 more entries, due to the calculation of
  "sizeof(*entry) + nr_entries * sizeof(long)", as the sizeof(*entry)
  now contains 8 entries.

  The size of the caller field needs to be subtracted from the size of
  the entry to create the correct allocation size"

* tag 'trace-v5.12-rc5-2' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace:
  tracing: Fix stack trace event size

kernel/trace/trace.c

@@ -2984,7 +2984,8 @@ static void __ftrace_trace_stack(struct trace_buffer *buffer,
 
 	size = nr_entries * sizeof(unsigned long);
 	event = __trace_buffer_lock_reserve(buffer, TRACE_STACK,
-					    sizeof(*entry) + size, trace_ctx);
+				    (sizeof(*entry) - sizeof(entry->caller)) + size,
+				    trace_ctx);
 	if (!event)
 		goto out;
 	entry = ring_buffer_event_data(event);