Re: Badness at kernel/rcutree.c:1228

[kordex - <kordex@gmail.com>]

Hey,

I put the debug function under init/main.c after rcu_init(); but there
is no output on dmesg which means that it receives zero value.

Full dmesg: http://xnet.fi/opt/apps/lkml-2.6.32-vanilla.dmesg.rcu-init.txt

--Mikko Kortelainen

2009/12/8 Paul E. McKenney <paulmck@linux.vnet.ibm.com>:
> On Tue, Dec 08, 2009 at 11:22:07AM -0800, Paul E. McKenney wrote:
>> At this point, I must defer to those more skilled than I at diagnosing
>> early-boot problems.
>
> Well, that is silly on my part -- the problem seems to appear late in
> boot, and you had no problem capturing that portion of the boot log.
>
> So please see below for a patch providing a rcu_check_beenonline()
> function that, when called after rcu_init(), returns non-zero if the
> beenonline fields have become corrupted.  So put calls of the form:
>
>        WARN_ON_ONCE(rcu_check_beenonline());
>
> in the initialization code path preceding the problem.  Either #include
> rcupdate.h or explicitly declare the function as appropriate.
>
> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> ---
>
> diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h
> index 9642c6b..190a687 100644
> --- a/include/linux/rcutree.h
> +++ b/include/linux/rcutree.h
> @@ -39,6 +39,8 @@ extern int rcu_cpu_notify(struct notifier_block *self,
>  extern int rcu_needs_cpu(int cpu);
>  extern int rcu_expedited_torture_stats(char *page);
>
> +extern int rcu_check_beenonline(void);
> +
>  #ifdef CONFIG_TREE_PREEMPT_RCU
>
>  extern void __rcu_read_lock(void);
> diff --git a/kernel/rcutree.c b/kernel/rcutree.c
> index 207125b..27d3722 100644
> --- a/kernel/rcutree.c
> +++ b/kernel/rcutree.c
> @@ -77,6 +77,17 @@ DEFINE_PER_CPU(struct rcu_data, rcu_sched_data);
>  struct rcu_state rcu_bh_state = RCU_STATE_INITIALIZER(rcu_bh_state);
>  DEFINE_PER_CPU(struct rcu_data, rcu_bh_data);
>
> +/*
> + * Ad-hoc diagnostic function, for use only after rcu_init() has
> + * returned.  Assumes that the boot CPU is CPU 0.  Assumes that
> + * the kernel has been built with CONFIG_TREE_RCU.  Not for inclusion.
> + * Usage: "WARN_ON_ONCE(rcu_check_beenonline());"
> + */
> +int rcu_check_beenonline(void)
> +{
> +       return !per_cpu(rcu_sched_data, 0).beenonline ||
> +              !per_cpu(rcu_bh_data, 0).beenonline;
> +}
>
>  /*
>  * Return true if an RCU grace period is in progress.  The ACCESS_ONCE()s
>