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Date: Thu, 31 Jul 2008 08:06:42 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Chirag Jog <chirag@...ux.vnet.ibm.com>
Cc: J?rgen Mell <j.mell@...nline.de>,
Thomas Gleixner <tglx@...utronix.de>,
LKML <linux-kernel@...r.kernel.org>,
rt-users <linux-rt-users@...r.kernel.org>,
Steven Rostedt <rostedt@...dmis.org>,
Clark Williams <williams@...hat.com>,
Josh Triplett <josht@...ux.vnet.ibm.com>,
"Timothy R. Chavez" <tim.chavez@...ux.vnet.ibm.com>
Subject: Re: [PATCH] Fix Bug messages
On Wed, 2008-07-30 at 22:48 +0530, Chirag Jog wrote:
> * J?rgen Mell <j.mell@...nline.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@...ux.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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