netdev - Re: [PATCH AUTOSEL 5.16 203/217] net: dsa: hold rtnl_mutex when calling dsa_master

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Date:   Tue, 18 Jan 2022 14:13:29 +0200
From:   Vladimir Oltean <olteanv@...il.com>
To:     Sasha Levin <sashal@...nel.org>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Vladimir Oltean <vladimir.oltean@....com>,
        Florian Fainelli <f.fainelli@...il.com>,
        "David S . Miller" <davem@...emloft.net>, andrew@...n.ch,
        vivien.didelot@...il.com, kuba@...nel.org, netdev@...r.kernel.org
Subject: Re: [PATCH AUTOSEL 5.16 203/217] net: dsa: hold rtnl_mutex when
 calling dsa_master_{setup,teardown}

Hi Sasha,

On Mon, Jan 17, 2022 at 09:19:26PM -0500, Sasha Levin wrote:
> From: Vladimir Oltean <vladimir.oltean@....com>
> 
> [ Upstream commit c146f9bc195a9dc3ad7fd000a14540e7c9df952d ]
> 
> DSA needs to simulate master tracking events when a binding is first
> with a DSA master established and torn down, in order to give drivers
> the simplifying guarantee that ->master_state_change calls are made
> only when the master's readiness state to pass traffic changes.
> master_state_change() provide a operational bool that DSA driver can use
> to understand if DSA master is operational or not.
> To avoid races, we need to block the reception of
> NETDEV_UP/NETDEV_CHANGE/NETDEV_GOING_DOWN events in the netdev notifier
> chain while we are changing the master's dev->dsa_ptr (this changes what
> netdev_uses_dsa(dev) reports).
> 
> The dsa_master_setup() and dsa_master_teardown() functions optionally
> require the rtnl_mutex to be held, if the tagger needs the master to be
> promiscuous, these functions call dev_set_promiscuity(). Move the
> rtnl_lock() from that function and make it top-level.
> 
> Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>
> Reviewed-by: Florian Fainelli <f.fainelli@...il.com>
> Signed-off-by: David S. Miller <davem@...emloft.net>
> Signed-off-by: Sasha Levin <sashal@...nel.org>
> ---

Please drop this patch from all stable branches (5.16, 5.15, 5.10).
Thanks.

>  net/dsa/dsa2.c   | 8 ++++++++
>  net/dsa/master.c | 4 ++--
>  2 files changed, 10 insertions(+), 2 deletions(-)
> 
> diff --git a/net/dsa/dsa2.c b/net/dsa/dsa2.c
> index 826957b6442b0..834f26539da73 100644
> --- a/net/dsa/dsa2.c
> +++ b/net/dsa/dsa2.c
> @@ -997,6 +997,8 @@ static int dsa_tree_setup_master(struct dsa_switch_tree *dst)
>  	struct dsa_port *dp;
>  	int err;
>  
> +	rtnl_lock();
> +
>  	list_for_each_entry(dp, &dst->ports, list) {
>  		if (dsa_port_is_cpu(dp)) {
>  			err = dsa_master_setup(dp->master, dp);
> @@ -1005,6 +1007,8 @@ static int dsa_tree_setup_master(struct dsa_switch_tree *dst)
>  		}
>  	}
>  
> +	rtnl_unlock();
> +
>  	return 0;
>  }
>  
> @@ -1012,9 +1016,13 @@ static void dsa_tree_teardown_master(struct dsa_switch_tree *dst)
>  {
>  	struct dsa_port *dp;
>  
> +	rtnl_lock();
> +
>  	list_for_each_entry(dp, &dst->ports, list)
>  		if (dsa_port_is_cpu(dp))
>  			dsa_master_teardown(dp->master);
> +
> +	rtnl_unlock();
>  }
>  
>  static int dsa_tree_setup_lags(struct dsa_switch_tree *dst)
> diff --git a/net/dsa/master.c b/net/dsa/master.c
> index e8e19857621bd..16b7dfd22bf5d 100644
> --- a/net/dsa/master.c
> +++ b/net/dsa/master.c
> @@ -267,9 +267,9 @@ static void dsa_master_set_promiscuity(struct net_device *dev, int inc)
>  	if (!ops->promisc_on_master)
>  		return;
>  
> -	rtnl_lock();
> +	ASSERT_RTNL();
> +
>  	dev_set_promiscuity(dev, inc);
> -	rtnl_unlock();
>  }
>  
>  static ssize_t tagging_show(struct device *d, struct device_attribute *attr,
> -- 
> 2.34.1
>