FAILED: patch "[PATCH] fgraph: Initialize tracing_graph_pause at task creation" failed to apply to 4.19-stable tree - Linux-stable-mirror

8 Feb 2021

The patch below does not apply to the 4.19-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to stable@vger.kernel.org.
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
...
From 7e0a9220467dbcfdc5bc62825724f3e52e50ab31 Mon Sep 17 00:00:00 2001
From: "Steven Rostedt (VMware)" rostedt@goodmis.org
Date: Fri, 29 Jan 2021 10:13:53 -0500
Subject: [PATCH] fgraph: Initialize tracing_graph_pause at task creation
On some archs, the idle task can call into cpu_suspend(). The cpu_suspend()
will disable or pause function graph tracing, as there's some paths in
bringing down the CPU that can have issues with its return address being
modified. The task_struct structure has a "tracing_graph_pause" atomic
counter, that when set to something other than zero, the function graph
tracer will not modify the return address.
The problem is that the tracing_graph_pause counter is initialized when the
function graph tracer is enabled. This can corrupt the counter for the idle
task if it is suspended in these architectures.
CPU 1				CPU 2
   -----				-----
  do_idle()
    cpu_suspend()
      pause_graph_tracing()
          task_struct->tracing_graph_pause++ (0 -> 1)
start_graph_tracing()
    			  for_each_online_cpu(cpu) {
    			    ftrace_graph_init_idle_task(cpu)
    			      task-struct->tracing_graph_pause = 0 (1 -> 0)
unpause_graph_tracing()
          task_struct->tracing_graph_pause-- (0 -> -1)
The above should have gone from 1 to zero, and enabled function graph
tracing again. But instead, it is set to -1, which keeps it disabled.
There's no reason that the field tracing_graph_pause on the task_struct can
not be initialized at boot up.
Cc: stable@vger.kernel.org
Fixes: 380c4b1411ccd ("tracing/function-graph-tracer: append the tracing_graph_flag")
Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=211339
Reported-by: pierre.gondois@arm.com
Signed-off-by: Steven Rostedt (VMware) rostedt@goodmis.org

diff --git a/init/init_task.c b/init/init_task.c
index 8a992d73e6fb..3711cdaafed2 100644
--- a/init/init_task.c
+++ b/init/init_task.c
@@ -198,7 +198,8 @@ struct task_struct init_task
    .lockdep_recursion = 0,
 #endif
 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
-	.ret_stack	= NULL,
+	.ret_stack		= NULL,
+	.tracing_graph_pause	= ATOMIC_INIT(0),
 #endif
 #if defined(CONFIG_TRACING) && defined(CONFIG_PREEMPTION)
    .trace_recursion = 0,
diff --git a/kernel/trace/fgraph.c b/kernel/trace/fgraph.c
index 73edb9e4f354..29a6ebeebc9e 100644
--- a/kernel/trace/fgraph.c
+++ b/kernel/trace/fgraph.c
@@ -394,7 +394,6 @@ static int alloc_retstack_tasklist(struct ftrace_ret_stack **ret_stack_list)
    	}
if (t->ret_stack == NULL) {
-			atomic_set(&t->tracing_graph_pause, 0);
    		atomic_set(&t->trace_overrun, 0);
    		t->curr_ret_stack = -1;
    		t->curr_ret_depth = -1;
@@ -489,7 +488,6 @@ static DEFINE_PER_CPU(struct ftrace_ret_stack *, idle_ret_stack);
 static void
 graph_init_task(struct task_struct *t, struct ftrace_ret_stack *ret_stack)
 {
-	atomic_set(&t->tracing_graph_pause, 0);
    atomic_set(&t->trace_overrun, 0);
    t->ftrace_timestamp = 0;
    /* make curr_ret_stack visible before we add the ret_stack */

    