netdev - Re: [PATCH v2] dummy: fix rcu_sched self-detected stalls

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Date:	Mon, 11 Jun 2012 09:51:15 -0700
From:	Stephen Hemminger <shemminger@...tta.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	David Miller <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [PATCH v2] dummy: fix rcu_sched self-detected stalls

On Mon, 11 Jun 2012 09:11:57 +0200
Eric Dumazet <eric.dumazet@...il.com> wrote:

> From: Eric Dumazet <edumazet@...gle.com>
> 
> Trying to "modprobe dummy numdummies=30000" triggers :
> 
> INFO: rcu_sched self-detected stall on CPU { 8} (t=60000 jiffies)
> 
> After this splat, RTNL is locked and reboot is needed.
> 
> We must call cond_resched() to avoid this, even holding RTNL.
> 
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> ---
>  drivers/net/dummy.c |    4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/net/dummy.c b/drivers/net/dummy.c
> index 442d91a..bab0158 100644
> --- a/drivers/net/dummy.c
> +++ b/drivers/net/dummy.c
> @@ -187,8 +187,10 @@ static int __init dummy_init_module(void)
>  	rtnl_lock();
>  	err = __rtnl_link_register(&dummy_link_ops);
>  
> -	for (i = 0; i < numdummies && !err; i++)
> +	for (i = 0; i < numdummies && !err; i++) {
>  		err = dummy_init_one();
> +		cond_resched();
> +	}
>  	if (err < 0)
>  		__rtnl_link_unregister(&dummy_link_ops);
>  	rtnl_unlock();
> 


Rather than holding lock for the whole loop, why not reacquire
each time to keep from holding off everything els.


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