linux-kernel - Re: [PATCH] Input: pxrc - simplify mutex handling with guard macro

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Date:   Fri, 1 Dec 2023 15:33:24 -0800
From:   Dmitry Torokhov <dmitry.torokhov@...il.com>
To:     Johan Hovold <johan@...nel.org>
Cc:     Marcus Folkesson <marcus.folkesson@...il.com>,
        linux-input@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Input: pxrc - simplify mutex handling with guard macro

On Fri, Dec 01, 2023 at 02:29:22PM +0100, Johan Hovold wrote:
> On Fri, Dec 01, 2023 at 01:08:45PM +0100, Marcus Folkesson wrote:
> > Use the guard(mutex) macro for handle mutex lock/unlocks.
> > 
> > Signed-off-by: Marcus Folkesson <marcus.folkesson@...il.com>
> 
> A couple of drive-by comments below.
> 
> > ---
> >  drivers/input/joystick/pxrc.c | 27 +++++++++++----------------
> >  1 file changed, 11 insertions(+), 16 deletions(-)
> > 
> > diff --git a/drivers/input/joystick/pxrc.c b/drivers/input/joystick/pxrc.c
> > index ea2bf5951d67..3c3bf7179b46 100644
> > --- a/drivers/input/joystick/pxrc.c
> > +++ b/drivers/input/joystick/pxrc.c
> > @@ -5,15 +5,17 @@
> >   * Copyright (C) 2018 Marcus Folkesson <marcus.folkesson@...il.com>
> >   */
> >  
> > -#include <linux/kernel.h>
> > +#include <linux/cleanup.h>
> >  #include <linux/errno.h>
> > -#include <linux/slab.h>
> > +#include <linux/input.h>
> > +#include <linux/kernel.h>
> >  #include <linux/module.h>
> > +#include <linux/mutex.h>
> > +#include <linux/slab.h>
> >  #include <linux/uaccess.h>
> > +
> >  #include <linux/usb.h>
> >  #include <linux/usb/input.h>
> > -#include <linux/mutex.h>
> > -#include <linux/input.h>
> 
> Looks like an unrelated change.
>   
> >  #define PXRC_VENDOR_ID		0x1781
> >  #define PXRC_PRODUCT_ID		0x0898
> > @@ -89,25 +91,20 @@ static int pxrc_open(struct input_dev *input)
> >  		dev_err(&pxrc->intf->dev,
> >  			"%s - usb_submit_urb failed, error: %d\n",
> >  			__func__, retval);
> > -		retval = -EIO;
> > -		goto out;
> > +		return -EIO;
> >  	}
> >  
> >  	pxrc->is_open = true;
> > -
> > -out:
> > -	mutex_unlock(&pxrc->pm_mutex);
> > -	return retval;
> > +	return 0;
> >  }
> 
> Eh, this looks obviously broken. Did you not test this before
> submitting? I assume lockdep would complain loudly too.
> 
> You're apparently the author of this driver and can test it, but I fear
> the coming onslaught of untested guard conversions from the "cleanup"
> crew. Not sure I find the result generally more readable either.

Yeah, for the code without conditions (like pxrc_close) the utility is
questionable, but I guess it is just a matter of getting used to the new
facilities...

Thanks.

-- 
Dmitry