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    SubjectRe: [PATCH] Fix Bug messages
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    Date
    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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