The patch below does not apply to the 4.4-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@xxxxxxxxxxxxxxx>.
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
>From 15516c89acce948debc4c598e03c3fee53045797 Mon Sep 17 00:00:00 2001
From: "Steven Rostedt (VMware)" <rostedt@xxxxxxxxxxx>
Date: Thu, 21 Sep 2017 13:00:21 -0400
Subject: [PATCH] tracing: Remove RCU work arounds from stack tracer
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.
Cc: stable@xxxxxxxxxxxxxxx
Fixes: 0be964be0 ("module: Sanitize RCU usage and locking")
Acked-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
Suggested-by: "Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>
diff --git a/kernel/trace/trace_stack.c b/kernel/trace/trace_stack.c
index a4df67cbc711..49cb41412eec 100644
--- a/kernel/trace/trace_stack.c
+++ b/kernel/trace/trace_stack.c
@@ -96,23 +96,9 @@ check_stack(unsigned long ip, unsigned long *stack)
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 long *stack)
}
out:
- rcu_irq_exit();
arch_spin_unlock(&stack_trace_max_lock);
local_irq_restore(flags);
}