linux-kernel - [for-next][PATCH 17/18] function_graph: Reverse the order of pushing the ret

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Date:   Wed, 21 Nov 2018 19:28:18 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     linux-kernel@...r.kernel.org
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        linux-arch@...r.kernel.org,
        Joel Fernandes <joel@...lfernandes.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Andy Lutomirski <luto@...nel.org>,
        Frederic Weisbecker <frederic@...nel.org>, stable@...nel.org
Subject: [for-next][PATCH 17/18] function_graph: Reverse the order of pushing the ret_stack and the
 callback

From: "Steven Rostedt (VMware)" <rostedt@...dmis.org>

The function graph profiler uses the ret_stack to store the "subtime" and
reuse it by nested functions and also on the return. But the current logic
has the profiler callback called before the ret_stack is updated, and it is
just modifying the ret_stack that will later be allocated (it's just lucky
that the "subtime" is not touched when it is allocated).

This could also cause a crash if we are at the end of the ret_stack when
this happens.

By reversing the order of the allocating the ret_stack and then calling the
callbacks attached to a function being traced, the ret_stack entry is no
longer used before it is allocated.

Cc: stable@...nel.org
Fixes: 03274a3ffb449 ("tracing/fgraph: Adjust fgraph depth before calling trace return callback")
Signed-off-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
---
 kernel/trace/trace_functions_graph.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/kernel/trace/trace_functions_graph.c b/kernel/trace/trace_functions_graph.c
index 4f0d72ae6362..2561460d7baf 100644
--- a/kernel/trace/trace_functions_graph.c
+++ b/kernel/trace/trace_functions_graph.c
@@ -188,15 +188,17 @@ int function_graph_enter(unsigned long ret, unsigned long func,
 	trace.func = func;
 	trace.depth = ++current->curr_ret_depth;
 
-	/* Only trace if the calling function expects to */
-	if (!ftrace_graph_entry(&trace))
-		goto out;
-
 	if (ftrace_push_return_trace(ret, func,
 				     frame_pointer, retp))
 		goto out;
 
+	/* Only trace if the calling function expects to */
+	if (!ftrace_graph_entry(&trace))
+		goto out_ret;
+
 	return 0;
+ out_ret:
+	current->curr_ret_stack--;
  out:
 	current->curr_ret_depth--;
 	return -EBUSY;
-- 
2.19.1