Re: [PATCH net-next v2 02/13] wifi: cfg80211: use __rtnl_unlock in nl80211_pre_doit

[Stanislav Fomichev <stfomichev@gmail.com>]

On 03/18, Stanislav Fomichev wrote:
> nl80211_pre_doit acquires rtnl_lock and then wiphy_lock, releasing
> rtnl while keeping wiphy_lock held until post_doit. With the
> introduction of rx_mode_wq and its flush in netdev_run_todo, calling
> rtnl_unlock here creates a circular lock dependency:
> 
>   Chain exists of:
>     (wq_completion)rx_mode_wq --> rtnl_mutex --> &rdev->wiphy.mtx
> 
>    Possible unsafe locking scenario:
> 
>          CPU0                    CPU1
>          ----                    ----
>     lock(&rdev->wiphy.mtx);
>                                  lock(rtnl_mutex);
>                                  lock(&rdev->wiphy.mtx);
>     lock((wq_completion)rx_mode_wq);
> 
> Switch to __rtnl_unlock to skip netdev_run_todo in nl80211_pre_doit.
> This seems safe because we run before the op.
> 
> Link: http://lore.kernel.org/netdev/69b5ad67.a00a0220.3b25d1.001a.GAE@google.com
> Signed-off-by: Stanislav Fomichev <sdf@fomichev.me>
> ---
>  net/wireless/nl80211.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/net/wireless/nl80211.c b/net/wireless/nl80211.c
> index 2225f5d0b124..ce5f25d4c87e 100644
> --- a/net/wireless/nl80211.c
> +++ b/net/wireless/nl80211.c
> @@ -18192,7 +18192,7 @@ static int nl80211_pre_doit(const struct genl_split_ops *ops,
>  		__release(&rdev->wiphy.mtx);
>  	}
>  	if (!(internal_flags & NL80211_FLAG_NEED_RTNL))
> -		rtnl_unlock();
> +		__rtnl_unlock();
>  
>  	return 0;
>  out_unlock:
> -- 
> 2.53.0
> 

ERROR: modpost: "__rtnl_unlock" [net/wireless/cfg80211.ko] undefined!

Gonna re-run local nipa ingest locally to see if anything else pops up.

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