netdev - Re: [PATCH 1/3] batman-adv: wait for rtnl in batadv_store_mesh

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Date:	Tue, 11 Jun 2013 15:09:30 +0100
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	Antonio Quartulli <ordex@...istici.org>
CC:	<davem@...emloft.net>, <netdev@...r.kernel.org>,
	<b.a.t.m.a.n@...ts.open-mesh.org>,
	Matthias Schiffer <mschiffer@...verse-factory.net>,
	Marek Lindner <lindner_marek@...oo.de>
Subject: Re: [PATCH 1/3] batman-adv: wait for rtnl in
 batadv_store_mesh_iface instead of failing if it is taken

On Tue, 2013-06-11 at 08:34 +0200, Antonio Quartulli wrote:
> From: Matthias Schiffer <mschiffer@...verse-factory.net>
> 
> The rtnl_lock in batadv_store_mesh_iface has been converted to a rtnl_trylock
> some time ago to avoid a possible deadlock between rtnl and s_active on removal
> of the sysfs nodes.
> 
> The behaviour introduced by that was quite confusing as it could lead to the
> sysfs store to fail, making batman-adv setup scripts unreliable.

I think what you actually wanted was ERESTARTNOINTR.  But the real
problem is that neither of these error codes is valid unless the system
call is aborted due to a signal.

Ben.

>  As recently the
> sysfs removal was postponed to a worker not running with the rtnl taken, the
> deadlock can't occur any more and it is safe to change the trylock back to a
> lock to make the sysfs store reliable again.
> 
> Signed-off-by: Matthias Schiffer <mschiffer@...verse-factory.net>
> Reviewed-by: Simon Wunderlich <siwu@....tu-chemnitz.de>
> Signed-off-by: Marek Lindner <lindner_marek@...oo.de>
> Signed-off-by: Antonio Quartulli <ordex@...istici.org>
> ---
>  net/batman-adv/sysfs.c | 5 +----
>  1 file changed, 1 insertion(+), 4 deletions(-)
> 
> diff --git a/net/batman-adv/sysfs.c b/net/batman-adv/sysfs.c
> index 15a22ef..929e304 100644
> --- a/net/batman-adv/sysfs.c
> +++ b/net/batman-adv/sysfs.c
> @@ -582,10 +582,7 @@ static ssize_t batadv_store_mesh_iface(struct kobject *kobj,
>  	    (strncmp(hard_iface->soft_iface->name, buff, IFNAMSIZ) == 0))
>  		goto out;
>  
> -	if (!rtnl_trylock()) {
> -		ret = -ERESTARTSYS;
> -		goto out;
> -	}
> +	rtnl_lock();
>  
>  	if (status_tmp == BATADV_IF_NOT_IN_USE) {
>  		batadv_hardif_disable_interface(hard_iface,

-- 
Ben Hutchings, Staff Engineer, Solarflare
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

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