Re: [PATCH] sched: add a stacktrace on enqueue_pushable error

[Gilles Carry <Gilles.Carry@bull.net>]

Hi,

I could reproduce the bug on an intel architecture.
I found where the problem is.
I'll post the patch in a few hours.

Gilles.

Gregory Haskins wrote:
> Hi Chirag,
>   Please apply this patch to your 26.5-rt9 tree for ppc64, enable
>   CONFIG_PROVE_LOCKING (which enables CONFIG_STACKTRACE) and give it a whirl.
>   If you get an oops, please post the console output.
> 
> Thanks!
> 
> -Greg
> 
> ------------------
> sched: add a stacktrace on enqueue_pushable error
> 
> NOT FOR INCLUSION!
> 
> This is to help debug an issue discovered by Chirag Jog in the thread
> 
> http://lkml.org/lkml/2008/9/25/189
> 
> Signed-off-by: Gregory Haskins <ghaskins@novell.com>
> ---
> 
>  include/linux/sched.h |    6 ++++++
>  kernel/sched_rt.c     |   20 +++++++++++++++++++-
>  2 files changed, 25 insertions(+), 1 deletions(-)
> 
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 67da014..53e8a6a 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -87,6 +87,7 @@ struct sched_param {
>  #include <linux/task_io_accounting.h>
>  #include <linux/kobject.h>
>  #include <linux/latencytop.h>
> +#include <linux/stacktrace.h>
>  
>  #include <asm/processor.h>
>  
> @@ -1170,6 +1171,11 @@ struct task_struct {
>  
>  	struct list_head tasks;
>  	struct plist_node pushable_tasks;
> +	struct {
> +		unsigned long data[15];
> +		struct stack_trace trace;
> +		pid_t pid;
> +	} pushable_stack;
>  
>  	/*
>  	 * ptrace_list/ptrace_children forms the list of my children
> diff --git a/kernel/sched_rt.c b/kernel/sched_rt.c
> index 57a0c0d..0e6a88c 100644
> --- a/kernel/sched_rt.c
> +++ b/kernel/sched_rt.c
> @@ -55,7 +55,25 @@ static void update_rt_migration(struct rq *rq)
>  
>  static void enqueue_pushable_task(struct rq *rq, struct task_struct *p)
>  {
> -	plist_del(&p->pushable_tasks, &rq->rt.pushable_tasks);
> +	if (plist_node_empty(&p->pushable_tasks)) {
> +		struct stack_trace *trace = &p->pushable_stack.trace;
> +
> +		trace->nr_entries = 0;
> +		trace->max_entries = sizeof(p->pushable_stack.data)/sizeof(p->pushable_stack.data[0]);
> +		trace->entries = &p->pushable_stack.data[0];
> +		trace->skip = 0;
> +
> +		save_stack_trace(trace);
> +
> +		p->pushable_stack.pid = current->pid;
> +	} else {
> +		printk(KERN_CRIT "redundant enqueue by %d detected\n",
> +		       p->pushable_stack.pid);
> +		print_stack_trace(&p->pushable_stack.trace, 5);
> +
> +		BUG_ON(!plist_node_empty(&p->pushable_tasks));
> +	}
> +
>  	plist_node_init(&p->pushable_tasks, p->prio);
>  	plist_add(&p->pushable_tasks, &rq->rt.pushable_tasks);
>  }
> 
> --
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> 

-- 
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Gilles.Carry
Linux Project team
mailto: gilles.carry@bull.net
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