From 962cfbceddf5f8ab0cf74b6bd7f4d47a3afab209 Mon Sep 17 00:00:00 2001
From: Yong Zhang <yong.zhang0@gmail.com>
Date: Sun, 16 Oct 2011 18:56:45 +0800
Subject: [PATCH 114/262] printk: Don't call printk_tick in printk_needs_cpu()
 on RT

printk_tick() can't be called in atomic context when RT is enabled,
otherwise below warning will show:

[  117.597095] BUG: sleeping function called from invalid context at kernel/rtmutex.c:645
[  117.597102] in_atomic(): 1, irqs_disabled(): 1, pid: 0, name: kworker/0:0
[  117.597111] Pid: 0, comm: kworker/0:0 Not tainted 3.0.6-rt17-00284-gb76d419-dirty #7
[  117.597116] Call Trace:
[  117.597131]  [<c06e3b61>] ? printk+0x1d/0x24
[  117.597142]  [<c01390b6>] __might_sleep+0xe6/0x110
[  117.597151]  [<c06e634c>] rt_spin_lock+0x1c/0x30
[  117.597158]  [<c0142f26>] __wake_up+0x26/0x60
[  117.597166]  [<c014c78e>] printk_tick+0x3e/0x40
[  117.597173]  [<c014c7b4>] printk_needs_cpu+0x24/0x30
[  117.597181]  [<c017ecc8>] tick_nohz_stop_sched_tick+0x2e8/0x410
[  117.597191]  [<c017305a>] ? sched_clock_idle_wakeup_event+0x1a/0x20
[  117.597201]  [<c010182a>] cpu_idle+0x4a/0xb0
[  117.597209]  [<c06e0b97>] start_secondary+0xd3/0xd7

Now this is a really rare case and it's very unlikely that we starve
an logbuf waiter that way.

Signed-off-by: Yong Zhang <yong.zhang0@gmail.com>
Link: http://lkml.kernel.org/r/1318762607-2261-4-git-send-email-yong.zhang0@gmail.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
 kernel/printk.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/printk.c b/kernel/printk.c
index 300952e..9a27a94 100644
--- a/kernel/printk.c
+++ b/kernel/printk.c
@@ -1298,8 +1298,8 @@ void printk_tick(void)
 
 int printk_needs_cpu(int cpu)
 {
-	if (cpu_is_offline(cpu))
-		printk_tick();
+	if (unlikely(cpu_is_offline(cpu)))
+		__this_cpu_write(printk_pending, 0);
 	return __this_cpu_read(printk_pending);
 }
 
-- 
1.7.10.4