Patch "tracing: Remove RCU work arounds from stack tracer" has been added to the 4.13-stable tree

Patch "tracing: Remove RCU work arounds from stack tracer" has been added to the 4.13-stable tree

[gregkh]

This is a note to let you know that I've just added the patch titled

    tracing: Remove RCU work arounds from stack tracer

to the 4.13-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     tracing-remove-rcu-work-arounds-from-stack-tracer.patch
and it can be found in the queue-4.13 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From 15516c89acce948debc4c598e03c3fee53045797 Mon Sep 17 00:00:00 2001
From: "Steven Rostedt (VMware)" <rostedt@goodmis.org>
Date: Thu, 21 Sep 2017 13:00:21 -0400
Subject: tracing: Remove RCU work arounds from stack tracer

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

commit 15516c89acce948debc4c598e03c3fee53045797 upstream.

Currently the stack tracer calls rcu_irq_enter() to make sure RCU
is watching when it records a stack trace. But if the stack tracer
is triggered while tracing inside of a rcu_irq_enter(), calling
rcu_irq_enter() unconditionally can be problematic.

The reason for having rcu_irq_enter() in the first place has been
fixed from within the saving of the stack trace code, and there's no
reason for doing it in the stack tracer itself. Just remove it.

Fixes: 0be964be0 ("module: Sanitize RCU usage and locking")
Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Suggested-by: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 kernel/trace/trace_stack.c |   15 ---------------
 1 file changed, 15 deletions(-)

--- a/kernel/trace/trace_stack.c
+++ b/kernel/trace/trace_stack.c
@@ -96,23 +96,9 @@ check_stack(unsigned long ip, unsigned l
 	if (in_nmi())
 		return;
 
-	/*
-	 * There's a slight chance that we are tracing inside the
-	 * RCU infrastructure, and rcu_irq_enter() will not work
-	 * as expected.
-	 */
-	if (unlikely(rcu_irq_enter_disabled()))
-		return;
-
 	local_irq_save(flags);
 	arch_spin_lock(&stack_trace_max_lock);
 
-	/*
-	 * RCU may not be watching, make it see us.
-	 * The stack trace code uses rcu_sched.
-	 */
-	rcu_irq_enter();
-
 	/* In case another CPU set the tracer_frame on us */
 	if (unlikely(!frame_size))
 		this_size -= tracer_frame;
@@ -205,7 +191,6 @@ check_stack(unsigned long ip, unsigned l
 	}
 
  out:
-	rcu_irq_exit();
 	arch_spin_unlock(&stack_trace_max_lock);
 	local_irq_restore(flags);
 }


Patches currently in stable-queue which might be from rostedt@goodmis.org are

queue-4.13/tracing-erase-irqsoff-trace-with-empty-write.patch
queue-4.13/tracing-fix-trace_pipe-behavior-for-instance-traces.patch
queue-4.13/genirq-fix-cpumask-check-in-__irq_startup_managed.patch
queue-4.13/tracing-remove-rcu-work-arounds-from-stack-tracer.patch