Re: [B.A.T.M.A.N.] [PATCHv2 3/3] batman-adv: Avoid deadlock between rtnl_lock and s_active

["Linus Lüssing" <linus.luessing@web.de>]

Looks good, seems to make sense and tried it. Works so far with no
call traces or other uggly stuff. However I'm still trying to
reproduce the initial issue of ticket #145 to confirm that this
patch fixes it (used a different kernel and batman-adv version
back then, of course... so somehow the 'always' stated there does
not seem to be valid anymore :) ).

PS: Ok, just sometimes I'm still getting a locking dependancy call
trace, but that one involves two different locks
((&(&bat_priv->hna_ghash_lock)->rlock){+.-...}, at: [<f83a3dd6>]
hna_global_del_orig+0x22/0x90 [batman_adv]
(&(&hash->list_locks[i])->rlock){+.-...}, at: [<f839fe4b>]
_purge_orig+0x45/0x1be [batman_adv]) and therefore seems to be
unrelated - I'll open a new ticket for that.

On Sat, Apr 30, 2011 at 06:57:00PM +0200, Sven Eckelmann wrote:
> The hard_if_event is called by the notifier with rtnl_lock and tries to
> remove sysfs entries when a NETDEV_UNREGISTER event is received. This
> will automatically take the s_active lock.
> 
> The s_active lock is also used when a new interface is added to a meshif
> through sysfs. In that situation we cannot wait for the rntl_lock before
> creating the actual batman-adv interface to prevent a deadlock. It is
> still possible to try to get the rtnl_lock and immediately abort the
> current operation when the trylock call failed.
> 
> Signed-off-by: Sven Eckelmann <sven@narfation.org>
> ---
> Remove '{' '}' after 'if (hard_iface->if_status != IF_NOT_IN_USE)'
> 
>  bat_sysfs.c      |   16 +++++++++-------
>  soft-interface.c |    2 +-
>  2 files changed, 10 insertions(+), 8 deletions(-)
> 
> diff --git a/bat_sysfs.c b/bat_sysfs.c
> index e449bf6..497a070 100644
> --- a/bat_sysfs.c
> +++ b/bat_sysfs.c
> @@ -488,22 +488,24 @@ static ssize_t store_mesh_iface(struct kobject *kobj, struct attribute *attr,
>  	    (strncmp(hard_iface->soft_iface->name, buff, IFNAMSIZ) == 0))
>  		goto out;
>  
> +	if (!rtnl_trylock()) {
> +		ret = -ERESTARTSYS;
> +		goto out;
> +	}
> +
>  	if (status_tmp == IF_NOT_IN_USE) {
> -		rtnl_lock();
>  		hardif_disable_interface(hard_iface);
> -		rtnl_unlock();
> -		goto out;
> +		goto unlock;
>  	}
>  
>  	/* if the interface already is in use */
> -	if (hard_iface->if_status != IF_NOT_IN_USE) {
> -		rtnl_lock();
> +	if (hard_iface->if_status != IF_NOT_IN_USE)
>  		hardif_disable_interface(hard_iface);
> -		rtnl_unlock();
> -	}
>  
>  	ret = hardif_enable_interface(hard_iface, buff);
>  
> +unlock:
> +	rtnl_unlock();
>  out:
>  	hardif_free_ref(hard_iface);
>  	return ret;
> diff --git a/soft-interface.c b/soft-interface.c
> index f4d80ad..bf53aa3 100644
> --- a/soft-interface.c
> +++ b/soft-interface.c
> @@ -613,7 +613,7 @@ struct net_device *softif_create(char *name)
>  		goto out;
>  	}
>  
> -	ret = register_netdev(soft_iface);
> +	ret = register_netdevice(soft_iface);
>  	if (ret < 0) {
>  		pr_err("Unable to register the batman interface '%s': %i\n",
>  		       name, ret);
> -- 
> 1.7.4.4
>