netdev - RE: [net-next 07/10] igb: Added rcu

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Date:	Wed, 26 Jun 2013 16:42:19 +0000
From:	"Abodunrin, Akeem G" <akeem.g.abodunrin@...el.com>
To:	Eric Dumazet <eric.dumazet@...il.com>,
	"Kirsher, Jeffrey T" <jeffrey.t.kirsher@...el.com>,
	"Duyck, Alexander H" <alexander.h.duyck@...el.com>
CC:	"davem@...emloft.net" <davem@...emloft.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"gospo@...hat.com" <gospo@...hat.com>,
	"sassmann@...hat.com" <sassmann@...hat.com>
Subject: RE: [net-next 07/10] igb: Added rcu_lock to avoid race



> -----Original Message-----
> From: Eric Dumazet [mailto:eric.dumazet@...il.com]
> Sent: Wednesday, June 26, 2013 4:20 AM
> To: Kirsher, Jeffrey T
> Cc: davem@...emloft.net; Abodunrin, Akeem G; netdev@...r.kernel.org;
> gospo@...hat.com; sassmann@...hat.com
> Subject: Re: [net-next 07/10] igb: Added rcu_lock to avoid race
> 
> On Wed, 2013-06-26 at 03:55 -0700, Jeff Kirsher wrote:
> > From: "Akeem G. Abodunrin" <akeem.g.abodunrin@...el.com>
> >
> > This patch adds rcu_lock to avoid possible race condition with
> > igb_update_stats function accessing the rings in free_ q_vector.
> >
> > Signed-off-by: Akeem G Abodunrin <akeem.g.abodunrin@...el.com>
> > Tested-by: Aaron Brown <aaron.f.brown@...el.com>
> > Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@...el.com>
> > ---
> >  drivers/net/ethernet/intel/igb/igb_main.c | 7 ++++++-
> >  1 file changed, 6 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/net/ethernet/intel/igb/igb_main.c
> > b/drivers/net/ethernet/intel/igb/igb_main.c
> > index 7112e52..c74ad78 100644
> > --- a/drivers/net/ethernet/intel/igb/igb_main.c
> > +++ b/drivers/net/ethernet/intel/igb/igb_main.c
> > @@ -705,6 +705,8 @@ static void __exit igb_exit_module(void)
> >  	dca_unregister_notify(&dca_notifier);
> >  #endif
> >  	pci_unregister_driver(&igb_driver);
> > +
> > +	rcu_barrier(); /* Wait for completion of call_rcu()'s */
> >  }
> >
> 
> This is not needed.
> 
> If this is really needed, a better comment would be welcomed ;)

Thanks Eric!

I believe we need this to make sure memory is released before removing driver code from the kernel, especially with each call to rcu - that is the reason for the comment "Wait for completion of call_rcu()'s".

Regards,
~Akeem

> 
> >  module_exit(igb_exit_module);
> > @@ -1013,7 +1015,7 @@ static void igb_free_q_vector(struct igb_adapter
> *adapter, int v_idx)
> >  	adapter->q_vector[v_idx] = NULL;
> >  	netif_napi_del(&q_vector->napi);
> >
> > -	/* ixgbe_get_stats64() might access the rings on this vector,
> > +	/* igb_get_stats64() might access the rings on this vector,
> >  	 * we must wait a grace period before freeing it.
> >  	 */
> >  	kfree_rcu(q_vector, rcu);
> > @@ -4860,6 +4862,8 @@ void igb_update_stats(struct igb_adapter
> > *adapter,
> >
> >  	bytes = 0;
> >  	packets = 0;
> > +
> > +	rcu_read_lock();
> >  	for (i = 0; i < adapter->num_rx_queues; i++) {
> >  		u32 rqdpc = rd32(E1000_RQDPC(i));
> >  		struct igb_ring *ring = adapter->rx_ring[i]; @@ -4895,6 +4899,7
> @@
> > void igb_update_stats(struct igb_adapter *adapter,
> >  	}
> >  	net_stats->tx_bytes = bytes;
> >  	net_stats->tx_packets = packets;
> > +	rcu_read_unlock();
> >
> >  	/* read stats registers */
> >  	adapter->stats.crcerrs += rd32(E1000_CRCERRS);
>