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Commit 160062e1 authored by Linus Torvalds's avatar Linus Torvalds
Browse files

Merge tag 'trace-v4.11-rc5-5' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace 

Pull two more ftrace fixes from Steven Rostedt:
 "While continuing my development, I uncovered two more small bugs.

  One is a race condition when enabling the snapshot function probe
  trigger. It enables the probe before allocating the snapshot, and if
  the probe triggers first, it stops tracing with a warning that the
  snapshot buffer was not allocated.

  The seconds is that the snapshot file should show how to use it when
  it is empty. But a bug fix from long ago broke the "is empty" test and
  the snapshot file no longer displays the help message"

* tag 'trace-v4.11-rc5-5' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace:
  ring-buffer: Have ring_buffer_iter_empty() return true when empty
  tracing: Allocate the snapshot buffer before enabling probe
parents 7f425895 78f7a45d

kernel/trace/ring_buffer.c

+14 −2
Original line number Diff line number Diff line
@@ -3405,11 +3405,23 @@ EXPORT_SYMBOL_GPL(ring_buffer_iter_reset); 
int ring_buffer_iter_empty(struct ring_buffer_iter *iter)

{

	struct ring_buffer_per_cpu *cpu_buffer;

	struct buffer_page *reader;

	struct buffer_page *head_page;

	struct buffer_page *commit_page;

	unsigned commit;



	cpu_buffer = iter->cpu_buffer;



	return iter->head_page == cpu_buffer->commit_page &&

		iter->head == rb_commit_index(cpu_buffer);

	/* Remember, trace recording is off when iterator is in use */

	reader = cpu_buffer->reader_page;

	head_page = cpu_buffer->head_page;

	commit_page = cpu_buffer->commit_page;

	commit = rb_page_commit(commit_page);



	return ((iter->head_page == commit_page && iter->head == commit) ||

		(iter->head_page == reader && commit_page == head_page &&

		 head_page->read == commit &&

		 iter->head == rb_page_commit(cpu_buffer->reader_page)));

}

EXPORT_SYMBOL_GPL(ring_buffer_iter_empty);

kernel/trace/trace.c

+5 −3
Original line number Diff line number Diff line
@@ -6733,11 +6733,13 @@ ftrace_trace_snapshot_callback(struct ftrace_hash *hash, 
		return ret;



 out_reg:

	ret = register_ftrace_function_probe(glob, ops, count);

	ret = alloc_snapshot(&global_trace);

	if (ret < 0)

		goto out;



	if (ret >= 0)

		alloc_snapshot(&global_trace);

	ret = register_ftrace_function_probe(glob, ops, count);



 out:

	return ret < 0 ? ret : 0;

}