Merge tag 'trace-v4.11-rc5-5' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace (160062e1) · Commits · 戴 / test

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

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;
		}

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