[RFC][PATCHv2 5/8] sysrq: switch to printk.emergency mode in unsafe places

[Sergey Senozhatsky]

It's not always possible/safe to wake_up() printk kernel
thread from sysrq (theoretically). Thus we better switch
printk() to emergency mode in some of the sysrq handlers,
which allows us to immediately flush pending kernel message
to the console.

This patch adds printk_emergency_begin/on sections.

Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@xxxxxxxxx>
Suggested-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
---
 drivers/tty/sysrq.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c
index c6fc7141d7b2..817dfb69914d 100644
--- a/drivers/tty/sysrq.c
+++ b/drivers/tty/sysrq.c
@@ -49,6 +49,7 @@
 #include <linux/syscalls.h>
 #include <linux/of.h>
 #include <linux/rcupdate.h>
+#include <linux/console.h>
 
 #include <asm/ptrace.h>
 #include <asm/irq_regs.h>
@@ -239,6 +240,7 @@ static DECLARE_WORK(sysrq_showallcpus, sysrq_showregs_othercpus);
 
 static void sysrq_handle_showallcpus(int key)
 {
+	printk_emergency_begin();
 	/*
 	 * Fall back to the workqueue based printing if the
 	 * backtrace printing did not succeed or the
@@ -253,6 +255,7 @@ static void sysrq_handle_showallcpus(int key)
 		}
 		schedule_work(&sysrq_showallcpus);
 	}
+	printk_emergency_end();
 }
 
 static struct sysrq_key_op sysrq_showallcpus_op = {
@@ -279,8 +282,10 @@ static struct sysrq_key_op sysrq_showregs_op = {
 
 static void sysrq_handle_showstate(int key)
 {
+	printk_emergency_begin();
 	show_state();
 	show_workqueue_state();
+	printk_emergency_end();
 }
 static struct sysrq_key_op sysrq_showstate_op = {
 	.handler	= sysrq_handle_showstate,
@@ -291,7 +296,9 @@ static struct sysrq_key_op sysrq_showstate_op = {
 
 static void sysrq_handle_showstate_blocked(int key)
 {
+	printk_emergency_begin();
 	show_state_filter(TASK_UNINTERRUPTIBLE);
+	printk_emergency_end();
 }
 static struct sysrq_key_op sysrq_showstate_blocked_op = {
 	.handler	= sysrq_handle_showstate_blocked,
-- 
2.12.2