linux-kernel - Re: [ 08/68] dummy: fix rcu

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Message-ID: <20120713140909.GA3185@herton-Z68MA-D2H-B3>
Date:	Fri, 13 Jul 2012 11:09:10 -0300
From:	Herton Ronaldo Krzesinski <herton.krzesinski@...onical.com>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	alan@...rguk.ukuu.org.uk, Eric Dumazet <edumazet@...gle.com>,
	"David S. Miller" <davem@...emloft.net>
Subject: Re: [ 08/68] dummy: fix rcu_sched self-detected stalls

On Thu, Jul 12, 2012 at 04:01:42PM -0700, Greg Kroah-Hartman wrote:
> From: Greg KH <gregkh@...uxfoundation.org>
> 
> 3.0-stable review patch.  If anyone has any objections, please let me know.
> 
> ------------------
> 
> 
> From: Eric Dumazet <edumazet@...gle.com>
> 
> [ Upstream commit 16b0dc29c1af9df341428f4c49ada4f626258082 ]
> 
> 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>
> Signed-off-by: David S. Miller <davem@...emloft.net>
> Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> ---
>  drivers/net/dummy.c |    4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> --- a/drivers/net/dummy.c
> +++ b/drivers/net/dummy.c
> @@ -186,8 +186,10 @@ 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();

This cherry-pick for 3.0 has the same problem as the one that was
proposed to 3.2, build fails on i386/arm:

linux-stable/drivers/net/dummy.c: In function 'dummy_init_module':
linux-stable/drivers/net/dummy.c:191:3: error: implicit declaration of function 'cond_resched' [-Werror=implicit-function-declaration]

This will need an include for linux/sched.h as in 3.2 (the same proposed
patch for 3.4 shouldn't be affected).

> +	}
>  	if (err < 0)
>  		__rtnl_link_unregister(&dummy_link_ops);
>  	rtnl_unlock();
> 
> 
> --
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-- 
[]'s
Herton
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