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

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Date:	Mon, 16 Jul 2012 08:46:58 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	Herton Ronaldo Krzesinski <herton.krzesinski@...onical.com>
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 Fri, Jul 13, 2012 at 11:09:10AM -0300, Herton Ronaldo Krzesinski wrote:
> 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).

Thanks, I've made that change now.

greg k-h
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