linux-kernel - [RFC][PATCH 02/14] fgraph: Have set_graph_notrace only affect function

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Date:   Wed, 21 Nov 2018 20:27:10 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     linux-kernel@...r.kernel.org
Cc:     Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Joel Fernandes <joel@...lfernandes.org>,
        Andy Lutomirski <luto@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Namhyung Kim <namhyung@...nel.org>
Subject: [RFC][PATCH 02/14] fgraph: Have set_graph_notrace only affect function_graph tracer

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

In order to make the function graph infrastructure more generic, there can
not be code specific for the function_graph tracer in the generic code. This
includes the set_graph_notrace logic, that stops all graph calls when a
function in the set_graph_notrace is hit.

By using the trace_recursion mask, we can use a bit in the current
task_struct to implement the notrace code, and move the logic out of
fgraph.c and into trace_functions_graph.c and keeps it affecting only the
tracer and not all call graph callbacks.

Cc: Namhyung Kim <namhyung@...nel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
---
 kernel/trace/fgraph.c                | 21 ---------------------
 kernel/trace/trace.h                 |  6 ++++++
 kernel/trace/trace_functions_graph.c | 21 +++++++++++++++++++++
 3 files changed, 27 insertions(+), 21 deletions(-)

diff --git a/kernel/trace/fgraph.c b/kernel/trace/fgraph.c
index e8fcf1b2b38c..c684968b87e7 100644
--- a/kernel/trace/fgraph.c
+++ b/kernel/trace/fgraph.c
@@ -64,30 +64,9 @@ ftrace_push_return_trace(unsigned long ret, unsigned long func,
 		return -EBUSY;
 	}
 
-	/*
-	 * The curr_ret_stack is an index to ftrace return stack of
-	 * current task.  Its value should be in [0, FTRACE_RETFUNC_
-	 * DEPTH) when the function graph tracer is used.  To support
-	 * filtering out specific functions, it makes the index
-	 * negative by subtracting huge value (FTRACE_NOTRACE_DEPTH)
-	 * so when it sees a negative index the ftrace will ignore
-	 * the record.  And the index gets recovered when returning
-	 * from the filtered function by adding the FTRACE_NOTRACE_
-	 * DEPTH and then it'll continue to record functions normally.
-	 *
-	 * The curr_ret_stack is initialized to -1 and get increased
-	 * in this function.  So it can be less than -1 only if it was
-	 * filtered out via ftrace_graph_notrace_addr() which can be
-	 * set from set_graph_notrace file in tracefs by user.
-	 */
-	if (current->curr_ret_stack < -1)
-		return -EBUSY;
-
 	calltime = trace_clock_local();
 
 	index = ++current->curr_ret_stack;
-	if (ftrace_graph_notrace_addr(func))
-		current->curr_ret_stack -= FTRACE_NOTRACE_DEPTH;
 	barrier();
 	current->ret_stack[index].ret = ret;
 	current->ret_stack[index].func = func;
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 3b8c0e24ab30..f3ad85830961 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -512,6 +512,12 @@ enum {
  * can only be modified by current, we can reuse trace_recursion.
  */
 	TRACE_IRQ_BIT,
+/*
+ * To implement set_graph_notrace, if this bit is set, we ignore
+ * function graph tracing of called functions, until the return
+ * function is called to clear it.
+ */
+	TRACE_GRAPH_NOTRACE_BIT,
 };
 
 #define trace_recursion_set(bit)	do { (current)->trace_recursion |= (1<<(bit)); } while (0)
diff --git a/kernel/trace/trace_functions_graph.c b/kernel/trace/trace_functions_graph.c
index af1759cd6eab..4748dc1bf5e1 100644
--- a/kernel/trace/trace_functions_graph.c
+++ b/kernel/trace/trace_functions_graph.c
@@ -188,6 +188,18 @@ int trace_graph_entry(struct ftrace_graph_ent *trace)
 	int cpu;
 	int pc;
 
+	if (trace_recursion_test(TRACE_GRAPH_NOTRACE_BIT))
+		return 0;
+
+	if (ftrace_graph_notrace_addr(trace->func)) {
+		trace_recursion_set(TRACE_GRAPH_NOTRACE_BIT);
+		/*
+		 * Need to return 1 to have the return called
+		 * that will clear the NOTRACE bit.
+		 */
+		return 1;
+	}
+
 	if (!ftrace_trace_task(tr))
 		return 0;
 
@@ -288,6 +300,11 @@ void trace_graph_return(struct ftrace_graph_ret *trace)
 	int cpu;
 	int pc;
 
+	if (trace_recursion_test(TRACE_GRAPH_NOTRACE_BIT)) {
+		trace_recursion_clear(TRACE_GRAPH_NOTRACE_BIT);
+		return;
+	}
+
 	local_irq_save(flags);
 	cpu = raw_smp_processor_id();
 	data = per_cpu_ptr(tr->trace_buffer.data, cpu);
@@ -311,6 +328,10 @@ void set_graph_array(struct trace_array *tr)
 
 static void trace_graph_thresh_return(struct ftrace_graph_ret *trace)
 {
+	if (trace_recursion_test(TRACE_GRAPH_NOTRACE_BIT)) {
+		trace_recursion_clear(TRACE_GRAPH_NOTRACE_BIT);
+		return;
+	}
 	if (tracing_thresh &&
 	    (trace->rettime - trace->calltime < tracing_thresh))
 		return;
-- 
2.19.1