Subject: [PATCH RT 2/2][RFC] let RCU stall messages escape with CONFIG_PREEMPT_RT_FULL

From: [email-masked] (Frank Rowand)
Date: Tue, 4 Dec 2012 20:52:21 -0800

The printk()s in RCU stall warnings do not get flushed to the console
on ARM.  Add the oops_in_progress flag back into the special trylock case in
console_trylock_for_printk(), and set the flag using "bust_spinlocks(1)".
This allows the printk() output to be flushed to the console.

Signed-off-by: Frank Rowand <[email-masked]>
---
 kernel/printk.c  |    5 	3 +	2 -	0 !
 kernel/rcutree.c |   14 	14 +	0 -	0 !
 2 files changed, 17 insertions(+), 2 deletions(-)

Index: b/kernel/printk.c
===================================================================
--- a/kernel/printk.c
+++ b/kernel/printk.c
@@ -1390,8 +1390,9 @@ static int console_trylock_for_printk(un
 {
 	int retval = 0, wake = 0;
 #ifdef CONFIG_PREEMPT_RT_FULL
-	int lock = !early_boot_irqs_disabled && !irqs_disabled_flags(flags) &&
-		(preempt_count() <= 1);
+	int lock = oops_in_progress || (
+		!early_boot_irqs_disabled && !irqs_disabled_flags(flags) &&
+		(preempt_count() <= 1));
 #else
 	int lock = 1;
 #endif
Index: b/kernel/rcutree.c
===================================================================
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -758,6 +758,11 @@ static void print_other_cpu_stall(struct
 	raw_spin_unlock_irqrestore(&rnp->lock, flags);
 
 	/*
+	 * Allow printk() to flush to device
+	 */
+	bust_spinlocks(1);
+
+	/*
 	 * OK, time to rat on our buddy...
 	 * See Documentation/RCU/stallwarn.txt for info on how to debug
 	 * RCU CPU stall warnings.
@@ -799,6 +804,8 @@ static void print_other_cpu_stall(struct
 
 	rcu_print_detail_task_stall(rsp);
 
+	bust_spinlocks(0);
+
 	force_quiescent_state(rsp, 0);  /* Kick them all. */
 }
 
@@ -808,6 +815,11 @@ static void print_cpu_stall(struct rcu_s
 	struct rcu_node *rnp = rcu_get_root(rsp);
 
 	/*
+	 * Allow printk() to flush to device
+	 */
+	bust_spinlocks(1);
+
+	/*
 	 * OK, time to rat on ourselves...
 	 * See Documentation/RCU/stallwarn.txt for info on how to debug
 	 * RCU CPU stall warnings.
@@ -820,6 +832,8 @@ static void print_cpu_stall(struct rcu_s
 	if (!trigger_all_cpu_backtrace())
 		dump_stack();
 
+	bust_spinlocks(0);
+
 	raw_spin_lock_irqsave(&rnp->lock, flags);
 	if (ULONG_CMP_GE(jiffies, rsp->jiffies_stall))
 		rsp->jiffies_stall = jiffies +