netdev - Re: [PATCH] net: remove the unnecessary list

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Date:	Mon, 25 Feb 2013 17:04:23 +0800
From:	Gao feng <gaofeng@...fujitsu.com>
To:	David Miller <davem@...emloft.net>
CC:	netdev@...r.kernel.org
Subject: Re: [PATCH] net: remove the unnecessary list_del

On 2013/02/25 16:12, David Miller wrote:
> From: Gao feng <gaofeng@...fujitsu.com>
> Date: Mon, 25 Feb 2013 16:01:24 +0800
> 
>> I think it's better to make sure netdevice objects have valid pointers
>> by calling list_del in unregister_netdevice_many.
> 
> Please, for the sake of understanding, read the commit below.  And
> please make such necessary research in the future and reference any
> such commits in your proposed patch, as well as explaining why those
> commits in the past were wrong and why you're reverting of them is
> correct.
> 
> Just saying "this isn't necessary" is a very disappointing explanation
> for something as very non-trivial as this is.

Get it, sorry for the noise :(
Will do more research before making patch.

Thanks, the commit below is very useful.

> 
> Thank you.
> 
> commit ceaaec98ad99859ac90ac6863ad0a6cd075d8e0e
> Author: Eric Dumazet <eric.dumazet@...il.com>
> Date:   Thu Feb 17 22:59:19 2011 +0000
> 
>     net: deinit automatic LIST_HEAD
>     
>     commit 9b5e383c11b08784 (net: Introduce
>     unregister_netdevice_many()) left an active LIST_HEAD() in
>     rollback_registered(), with possible memory corruption.
>     
>     Even if device is freed without touching its unreg_list (and therefore
>     touching the previous memory location holding LISTE_HEAD(single), better
>     close the bug for good, since its really subtle.
>     
>     (Same fix for default_device_exit_batch() for completeness)
>     
>     Reported-by: Michal Hocko <mhocko@...e.cz>
>     Tested-by: Michal Hocko <mhocko@...e.cz>
>     Reported-by: Eric W. Biderman <ebiderman@...ssion.com>
>     Tested-by: Eric W. Biderman <ebiderman@...ssion.com>
>     Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
>     Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>
>     CC: Ingo Molnar <mingo@...e.hu>
>     CC: Octavian Purdila <opurdila@...acom.com>
>     CC: stable <stable@...nel.org> [.33+]
>     Signed-off-by: David S. Miller <davem@...emloft.net>
> 
> diff --git a/net/core/dev.c b/net/core/dev.c
> index a18c164..8ae6631 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -5066,6 +5066,7 @@ static void rollback_registered(struct net_device *dev)
>  
>  	list_add(&dev->unreg_list, &single);
>  	rollback_registered_many(&single);
> +	list_del(&single);
>  }
>  
>  unsigned long netdev_fix_features(unsigned long features, const char *name)
> @@ -6219,6 +6220,7 @@ static void __net_exit default_device_exit_batch(struct list_head *net_list)
>  		}
>  	}
>  	unregister_netdevice_many(&dev_kill_list);
> +	list_del(&dev_kill_list);
>  	rtnl_unlock();
>  }
>  
> --
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