Re: [PATCH] Fix Bug messages

[Peter Zijlstra <peterz@infradead.org>]

On Wed, 2008-07-30 at 22:48 +0530, Chirag Jog wrote:
> * J?rgen Mell <j.mell@t-online.de> [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

Looks sane, thanks Chirag!

> Signed-Off-By: Chirag <chirag@linux.vnet.ibm.com>
> 
> 
> 
> 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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