Subject: Re: [PATCH net] net: dsa: ocelot: call dsa_tag_8021q_unregister() under rtnl_lock() on driver remove

From: Simon Horman <[email-masked]>
Date: Thu, 3 Aug 2023 21:29:38 +0200

On Thu, Aug 03, 2023 at 04:42:53PM +0300, Vladimir Oltean wrote:
> When the tagging protocol in current use is "ocelot-8021q" and we unbind
> the driver, we see this splat:
> 
> $ echo '0000:00:00.2' > /sys/bus/pci/drivers/fsl_enetc/unbind
> mscc_felix 0000:00:00.5 swp0: left promiscuous mode
> sja1105 spi2.0: Link is Down
> DSA: tree 1 torn down
> mscc_felix 0000:00:00.5 swp2: left promiscuous mode
> sja1105 spi2.2: Link is Down
> DSA: tree 3 torn down
> fsl_enetc 0000:00:00.2 eno2: left promiscuous mode
> mscc_felix 0000:00:00.5: Link is Down
> ------------[ cut here ]------------
> RTNL: assertion failed at net/dsa/tag_8021q.c (409)
> WARNING: CPU: 1 PID: 329 at net/dsa/tag_8021q.c:409 dsa_tag_8021q_unregister+0x12c/0x1a0
> Modules linked in:
> CPU: 1 PID: 329 Comm: bash Not tainted 6.5.0-rc3+ #771
> pc : dsa_tag_8021q_unregister+0x12c/0x1a0
> lr : dsa_tag_8021q_unregister+0x12c/0x1a0
> Call trace:
>  dsa_tag_8021q_unregister+0x12c/0x1a0
>  felix_tag_8021q_teardown+0x130/0x150
>  felix_teardown+0x3c/0xd8
>  dsa_tree_teardown_switches+0xbc/0xe0
>  dsa_unregister_switch+0x168/0x260
>  felix_pci_remove+0x30/0x60
>  pci_device_remove+0x4c/0x100
>  device_release_driver_internal+0x188/0x288
>  device_links_unbind_consumers+0xfc/0x138
>  device_release_driver_internal+0xe0/0x288
>  device_driver_detach+0x24/0x38
>  unbind_store+0xd8/0x108
>  drv_attr_store+0x30/0x50
> ---[ end trace 0000000000000000 ]---
> ------------[ cut here ]------------
> RTNL: assertion failed at net/8021q/vlan_core.c (376)
> WARNING: CPU: 1 PID: 329 at net/8021q/vlan_core.c:376 vlan_vid_del+0x1b8/0x1f0
> CPU: 1 PID: 329 Comm: bash Tainted: G        W          6.5.0-rc3+ #771
> pc : vlan_vid_del+0x1b8/0x1f0
> lr : vlan_vid_del+0x1b8/0x1f0
>  dsa_tag_8021q_unregister+0x8c/0x1a0
>  felix_tag_8021q_teardown+0x130/0x150
>  felix_teardown+0x3c/0xd8
>  dsa_tree_teardown_switches+0xbc/0xe0
>  dsa_unregister_switch+0x168/0x260
>  felix_pci_remove+0x30/0x60
>  pci_device_remove+0x4c/0x100
>  device_release_driver_internal+0x188/0x288
>  device_links_unbind_consumers+0xfc/0x138
>  device_release_driver_internal+0xe0/0x288
>  device_driver_detach+0x24/0x38
>  unbind_store+0xd8/0x108
>  drv_attr_store+0x30/0x50
> DSA: tree 0 torn down
> 
> This was somewhat not so easy to spot, because "ocelot-8021q" is not the
> default tagging protocol, and thus, not everyone who tests the unbinding
> path may have switched to it beforehand. The default
> felix_tag_npi_teardown() does not require rtnl_lock() to be held.
> 
> Fixes: 7c83a7c539ab ("net: dsa: add a second tagger for Ocelot switches based on tag_8021q")
> Signed-off-by: Vladimir Oltean <[email-masked]>
> ---
>  drivers/net/dsa/ocelot/felix.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/net/dsa/ocelot/felix.c b/drivers/net/dsa/ocelot/felix.c
> index fd7eb4a52918..9a3e5ec16972 100644
> --- a/drivers/net/dsa/ocelot/felix.c
> +++ b/drivers/net/dsa/ocelot/felix.c
> @@ -1619,8 +1619,10 @@ static void felix_teardown(struct dsa_switch *ds)
>  	struct felix *felix = ocelot_to_felix(ocelot);
>  	struct dsa_port *dp;
>  
> +	rtnl_lock();
>  	if (felix->tag_proto_ops)
>  		felix->tag_proto_ops->teardown(ds);
> +	rtnl_unlock();

Hi Vladimir,

I am curious to know if RTNL could be taken in
felix_tag_8021q_teardown() instead.

>  
>  	dsa_switch_for_each_available_port(dp, ds)
>  		ocelot_deinit_port(ocelot, dp->index);
> -- 
> 2.34.1
> 
>