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

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 <[email protected]> know about it.

From: "Steven Rostedt (VMware)" <[email protected]>
Date: Thu, 21 Sep 2017 13:00:21 -0400
Subject: tracing: Remove RCU work arounds from stack tracer

From: Steven Rostedt (VMware) <[email protected]>

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.

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

@@ -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 [email protected] 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