linux-kernel - Re: [PATCH] usb: typec: fusb302: Fix debugfs mutex initialisation

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Message-ID: <20190318153922.GA16173@roeck-us.net>
Date:   Mon, 18 Mar 2019 08:39:22 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Marc Zyngier <marc.zyngier@....com>
Cc:     Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] usb: typec: fusb302: Fix debugfs mutex initialisation

On Mon, Mar 18, 2019 at 03:06:00PM +0000, Marc Zyngier wrote:
> Running a kernel with the fusb302 driver and lockdep enabled
> leads to an unpleasant warning:
> 
> [    4.617477] INFO: trying to register non-static key.
> [    4.617930] the code is fine but needs lockdep annotation.
> [    4.618418] turning off the locking correctness validator.
> [    4.618913] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.1.0-rc1-00007-g3542533f3fc9 #13
> [    4.619620] Hardware name: rockchip evb_rk3399/evb_rk3399, BIOS 2019.04-rc3-00124-g2feec69fb1 03/15/2019
> [    4.620454] Call trace:
> [    4.620693]  dump_backtrace+0x0/0x138
> [    4.621028]  show_stack+0x24/0x30
> [    4.621336]  dump_stack+0xbc/0x104
> [    4.621649]  register_lock_class+0x594/0x598
> [    4.622036]  __lock_acquire+0x80/0x11b8
> [    4.622384]  lock_acquire+0xdc/0x260
> [    4.622711]  __mutex_lock+0x90/0x8a0
> [    4.623037]  mutex_lock_nested+0x3c/0x50
> [    4.623394]  _fusb302_log+0x88/0x1f0
> [    4.623721]  fusb302_log+0x7c/0xa0
> [    4.624033]  tcpm_init+0x5c/0x190
> [    4.624336]  tcpm_init+0x3c/0x130
> [    4.624640]  tcpm_register_port+0x574/0x878
> [    4.625019]  fusb302_probe+0x2c8/0x590
> 
> Despite what the message says, the code isn't fine, as it tries to
> make use of the fusb302_log facility pretty early. This requires the
> logbuffer_lock mutex to be initialised, but that only happens much
> later. Boo.
> 
> Hoist the fusb302_debugfs_init call before tcpm_register_port so that
> we can enjoy a working mutex.
> 
> Signed-off-by: Marc Zyngier <marc.zyngier@....com>
> ---
>  drivers/usb/typec/tcpm/fusb302.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/usb/typec/tcpm/fusb302.c b/drivers/usb/typec/tcpm/fusb302.c
> index e9344997329c..7e3f8901daf6 100644
> --- a/drivers/usb/typec/tcpm/fusb302.c
> +++ b/drivers/usb/typec/tcpm/fusb302.c
> @@ -1790,6 +1790,7 @@ static int fusb302_probe(struct i2c_client *client,
>  			goto destroy_workqueue;
>  	}
>  
> +	fusb302_debugfs_init(chip);

This needs another error exit label right after destroy_workqueue,
and an added call to fusb302_debugfs_exit() after that label.

>  	chip->tcpm_port = tcpm_register_port(&client->dev, &chip->tcpc_dev);
>  	if (IS_ERR(chip->tcpm_port)) {
>  		ret = PTR_ERR(chip->tcpm_port);
> @@ -1807,7 +1808,6 @@ static int fusb302_probe(struct i2c_client *client,
>  		goto tcpm_unregister_port;
>  	}
>  	enable_irq_wake(chip->gpio_int_n_irq);
> -	fusb302_debugfs_init(chip);
>  	i2c_set_clientdata(client, chip);
>  
>  	return ret;
> -- 
> 2.20.1
>