netdev - Re: [PATCH net 1/7] net: dsa: mv88e6xxx: don't use devres for mdiobus

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Date:   Mon, 7 Feb 2022 18:45:54 -0800
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Vladimir Oltean <vladimir.oltean@....com>, netdev@...r.kernel.org
Cc:     Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Vladimir Oltean <olteanv@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Hauke Mehrtens <hauke@...ke-m.de>,
        Sean Wang <sean.wang@...iatek.com>,
        Landen Chao <Landen.Chao@...iatek.com>,
        DENG Qingfang <dqfext@...il.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Claudiu Manoil <claudiu.manoil@....com>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        UNGLinuxDriver@...rochip.com,
        Oleksij Rempel <linux@...pel-privat.de>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Laurentiu Tudor <laurentiu.tudor@....com>,
        Rafael Richter <rafael.richter@....de>,
        Daniel Klauer <daniel.klauer@....de>
Subject: Re: [PATCH net 1/7] net: dsa: mv88e6xxx: don't use devres for mdiobus



On 2/7/2022 8:15 AM, Vladimir Oltean wrote:
> As explained in commits:
> 74b6d7d13307 ("net: dsa: realtek: register the MDIO bus under devres")
> 5135e96a3dd2 ("net: dsa: don't allocate the slave_mii_bus using devres")
> 
> mdiobus_free() will panic when called from devm_mdiobus_free() <-
> devres_release_all() <- __device_release_driver(), and that mdiobus was
> not previously unregistered.
> 
> The mv88e6xxx is an MDIO device, so the initial set of constraints that
> I thought would cause this (I2C or SPI buses which call ->remove on
> ->shutdown) do not apply. But there is one more which applies here.
> 
> If the DSA master itself is on a bus that calls ->remove from ->shutdown
> (like dpaa2-eth, which is on the fsl-mc bus), there is a device link
> between the switch and the DSA master, and device_links_unbind_consumers()
> will unbind the Marvell switch driver on shutdown.
> 
> systemd-shutdown[1]: Powering off.
> mv88e6085 0x0000000008b96000:00 sw_gl0: Link is Down
> fsl-mc dpbp.9: Removing from iommu group 7
> fsl-mc dpbp.8: Removing from iommu group 7
> ------------[ cut here ]------------
> kernel BUG at drivers/net/phy/mdio_bus.c:677!
> Internal error: Oops - BUG: 0 [#1] PREEMPT SMP
> Modules linked in:
> CPU: 0 PID: 1 Comm: systemd-shutdow Not tainted 5.16.5-00040-gdc05f73788e5 #15
> pc : mdiobus_free+0x44/0x50
> lr : devm_mdiobus_free+0x10/0x20
> Call trace:
>   mdiobus_free+0x44/0x50
>   devm_mdiobus_free+0x10/0x20
>   devres_release_all+0xa0/0x100
>   __device_release_driver+0x190/0x220
>   device_release_driver_internal+0xac/0xb0
>   device_links_unbind_consumers+0xd4/0x100
>   __device_release_driver+0x4c/0x220
>   device_release_driver_internal+0xac/0xb0
>   device_links_unbind_consumers+0xd4/0x100
>   __device_release_driver+0x94/0x220
>   device_release_driver+0x28/0x40
>   bus_remove_device+0x118/0x124
>   device_del+0x174/0x420
>   fsl_mc_device_remove+0x24/0x40
>   __fsl_mc_device_remove+0xc/0x20
>   device_for_each_child+0x58/0xa0
>   dprc_remove+0x90/0xb0
>   fsl_mc_driver_remove+0x20/0x5c
>   __device_release_driver+0x21c/0x220
>   device_release_driver+0x28/0x40
>   bus_remove_device+0x118/0x124
>   device_del+0x174/0x420
>   fsl_mc_bus_remove+0x80/0x100
>   fsl_mc_bus_shutdown+0xc/0x1c
>   platform_shutdown+0x20/0x30
>   device_shutdown+0x154/0x330
>   kernel_power_off+0x34/0x6c
>   __do_sys_reboot+0x15c/0x250
>   __arm64_sys_reboot+0x20/0x30
>   invoke_syscall.constprop.0+0x4c/0xe0
>   do_el0_svc+0x4c/0x150
>   el0_svc+0x24/0xb0
>   el0t_64_sync_handler+0xa8/0xb0
>   el0t_64_sync+0x178/0x17c
> 
> So the same treatment must be applied to all DSA switch drivers, which
> is: either use devres for both the mdiobus allocation and registration,
> or don't use devres at all.
> 
> The Marvell driver already has a good structure for mdiobus removal, so
> just plug in mdiobus_free and get rid of devres.
> 
> Fixes: ac3a68d56651 ("net: phy: don't abuse devres in devm_mdiobus_register()")
> Reported-by: Rafael Richter <Rafael.Richter@....de>
> Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>

Reviewed-by: Florian Fainelli <f.fainelli@...il.com>
-- 
Florian