[PATCH] Fix Bug messages

[Chirag Jog]

* J?rgen Mell <j.mell@xxxxxxxxxxx> [2008-07-30 11:01:32]:

> Hello Thomas,
> 
> On Wednesday, 30. July 2008, Thomas Gleixner wrote:
> > We are pleased to announce the 2.6.26-rt1 tree, which can be
> > downloaded from the location:
> 
> I have tried the new kernel and have some good news and some bad news:
> 
> The good news: The machine boots and seems to run without major problems.
> 
> The bad news: It produces continuously lots of bug messages in the error 
> logs (cf. attached dmesg.tgz). The error at rtmutex.c:743 was already 
> present in 2.6.25-rt* when ACPI was enabled. The 'using smp_processor_id 
> ()  in preemptible code' is new here with 2.6.26.
> 
> Machine is an old Athlon XP (single core) on an EPOX mainboard with VIA 
> chipset.
> 
> If I can help with testing, please let me know.
> 
> Bye,
>          Jürgen
> 
> 
This patch should solve some of the bug messages.
It does two things:
1. Change rt_runtime_lock to be a raw spinlock as the comment above it
says: it is nested inside the rq lock.

2. Change mnt_writers to be a per_cpu locked variable.
This eliminates the need for the codepath to disable preemption and
then potentially sleep, leading to the BUG messages

Signed-Off-By: Chirag <chirag@xxxxxxxxxxxxxxxxxx>



Index: linux-2.6.26-rt1/kernel/sched.c
===================================================================
--- linux-2.6.26-rt1.orig/kernel/sched.c	2008-07-30 22:37:19.000000000 +0530
+++ linux-2.6.26-rt1/kernel/sched.c	2008-07-30 22:37:24.000000000 +0530
@@ -208,7 +208,7 @@
 
 struct rt_bandwidth {
 	/* nests inside the rq lock: */
-	spinlock_t		rt_runtime_lock;
+	raw_spinlock_t		rt_runtime_lock;
 	ktime_t			rt_period;
 	u64			rt_runtime;
 	struct hrtimer		rt_period_timer;
@@ -472,7 +472,7 @@
 	u64 rt_time;
 	u64 rt_runtime;
 	/* Nests inside the rq lock: */
-	spinlock_t rt_runtime_lock;
+	raw_spinlock_t rt_runtime_lock;
 
 #ifdef CONFIG_RT_GROUP_SCHED
 	unsigned long rt_nr_boosted;
Index: linux-2.6.26-rt1/fs/namespace.c
===================================================================
--- linux-2.6.26-rt1.orig/fs/namespace.c	2008-07-30 22:39:30.000000000 +0530
+++ linux-2.6.26-rt1/fs/namespace.c	2008-07-30 22:39:36.000000000 +0530
@@ -178,13 +178,13 @@
 	unsigned long count;
 	struct vfsmount *mnt;
 } ____cacheline_aligned_in_smp;
-static DEFINE_PER_CPU(struct mnt_writer, mnt_writers);
+static DEFINE_PER_CPU_LOCKED(struct mnt_writer, mnt_writers);
 
 static int __init init_mnt_writers(void)
 {
 	int cpu;
 	for_each_possible_cpu(cpu) {
-		struct mnt_writer *writer = &per_cpu(mnt_writers, cpu);
+		struct mnt_writer *writer = &per_cpu_var_locked(mnt_writers, cpu);
 		spin_lock_init(&writer->lock);
 		lockdep_set_class(&writer->lock, &writer->lock_class);
 		writer->count = 0;
@@ -199,7 +199,7 @@
 	struct mnt_writer *cpu_writer;
 
 	for_each_possible_cpu(cpu) {
-		cpu_writer = &per_cpu(mnt_writers, cpu);
+		cpu_writer = &per_cpu_var_locked(mnt_writers, cpu);
 		spin_unlock(&cpu_writer->lock);
 	}
 }
@@ -251,8 +251,8 @@
 {
 	int ret = 0;
 	struct mnt_writer *cpu_writer;
-
-	cpu_writer = &get_cpu_var(mnt_writers);
+	int cpu = 0;
+	cpu_writer = &get_cpu_var_locked(mnt_writers, &cpu);
 	spin_lock(&cpu_writer->lock);
 	if (__mnt_is_readonly(mnt)) {
 		ret = -EROFS;
@@ -262,7 +262,7 @@
 	cpu_writer->count++;
 out:
 	spin_unlock(&cpu_writer->lock);
-	put_cpu_var(mnt_writers);
+	put_cpu_var_locked(mnt_writers, cpu);
 	return ret;
 }
 EXPORT_SYMBOL_GPL(mnt_want_write);
@@ -273,7 +273,7 @@
 	struct mnt_writer *cpu_writer;
 
 	for_each_possible_cpu(cpu) {
-		cpu_writer = &per_cpu(mnt_writers, cpu);
+		cpu_writer = &per_cpu_var_locked(mnt_writers, cpu);
 		spin_lock(&cpu_writer->lock);
 		__clear_mnt_count(cpu_writer);
 		cpu_writer->mnt = NULL;
@@ -332,8 +332,8 @@
 {
 	int must_check_underflow = 0;
 	struct mnt_writer *cpu_writer;
-
-	cpu_writer = &get_cpu_var(mnt_writers);
+	int cpu = 0;
+	cpu_writer = &get_cpu_var_locked(mnt_writers, &cpu);
 	spin_lock(&cpu_writer->lock);
 
 	use_cpu_writer_for_mount(cpu_writer, mnt);
@@ -360,7 +360,7 @@
 	 * __mnt_writers can underflow.  Without it,
 	 * we could theoretically wrap __mnt_writers.
 	 */
-	put_cpu_var(mnt_writers);
+	put_cpu_var_locked(mnt_writers, cpu);
 }
 EXPORT_SYMBOL_GPL(mnt_drop_write);
 
@@ -612,7 +612,7 @@
 	 * can come in.
 	 */
 	for_each_possible_cpu(cpu) {
-		struct mnt_writer *cpu_writer = &per_cpu(mnt_writers, cpu);
+		struct mnt_writer *cpu_writer = &per_cpu_var_locked(mnt_writers, cpu);
 		if (cpu_writer->mnt != mnt)
 			continue;
 		spin_lock(&cpu_writer->lock);


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