From 722773afd83209d4088d30946bc274f547528a0b Mon Sep 17 00:00:00 2001
From: Rik van Riel <riel@redhat.com>
Date: Fri, 6 Jun 2014 14:38:14 -0700
Subject: [PATCH] sysrq,rcu: suppress RCU stall warnings while sysrq runs

Some sysrq handlers can run for a long time, because they dump a lot of
data onto a serial console.  Having RCU stall warnings pop up in the
middle of them only makes the problem worse.

This patch temporarily disables RCU stall warnings while a sysrq request
is handled.

Signed-off-by: Rik van Riel <riel@redhat.com>
Suggested-by: Paul McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Madper Xie <cxie@redhat.com>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Richard Weinberger <richard@nod.at>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
 drivers/tty/sysrq.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c
index 7430e87d7352..454b65898e2c 100644
--- a/drivers/tty/sysrq.c
+++ b/drivers/tty/sysrq.c
@@ -46,6 +46,7 @@
 #include <linux/jiffies.h>
 #include <linux/syscalls.h>
 #include <linux/of.h>
+#include <linux/rcupdate.h>
 
 #include <asm/ptrace.h>
 #include <asm/irq_regs.h>
@@ -511,6 +512,7 @@ void __handle_sysrq(int key, bool check_mask)
 	int orig_log_level;
 	int i;
 
+	rcu_sysrq_start();
 	rcu_read_lock();
 	/*
 	 * Raise the apparent loglevel to maximum so that the sysrq header
@@ -554,6 +556,7 @@ void __handle_sysrq(int key, bool check_mask)
 		console_loglevel = orig_log_level;
 	}
 	rcu_read_unlock();
+	rcu_sysrq_end();
 }
 
 void handle_sysrq(int key)
-- 
2.20.1