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

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Date:   Mon, 18 Mar 2019 17:32:56 +0000
From:   Marc Zyngier <marc.zyngier@....com>
To:     Guenter Roeck <linux@...ck-us.net>
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, 18 Mar 2019 08:39:22 -0700
Guenter Roeck <linux@...ck-us.net> wrote:

> 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.

You do mean before destroy_workqueue, right? Otherwise, the error
handling doesn't nest properly... Something like this:

diff --git a/drivers/usb/typec/tcpm/fusb302.c b/drivers/usb/typec/tcpm/fusb302.c
index 7e3f8901daf6..76cb8be6f3eb 100644
--- a/drivers/usb/typec/tcpm/fusb302.c
+++ b/drivers/usb/typec/tcpm/fusb302.c
@@ -1796,7 +1796,7 @@ static int fusb302_probe(struct i2c_client *client,
 		ret = PTR_ERR(chip->tcpm_port);
 		if (ret != -EPROBE_DEFER)
 			dev_err(dev, "cannot register tcpm port, ret=%d", ret);
-		goto destroy_workqueue;
+		goto unregister_debugfs;
 	}
 
 	ret = devm_request_threaded_irq(chip->dev, chip->gpio_int_n_irq,
@@ -1814,6 +1814,8 @@ static int fusb302_probe(struct i2c_client *client,
 
 tcpm_unregister_port:
 	tcpm_unregister_port(chip->tcpm_port);
+unregister_debugfs:
+	fusb302_debugfs_exit(chip);
 destroy_workqueue:
 	destroy_workqueue(chip->wq);
 
Thanks,

	M.
-- 
Without deviation from the norm, progress is not possible.