Re: [PATCH 2/2] gpio: gpiolib: set gpiochip_remove retval to void

From: Dan Carpenter <dan.carpenter@oracle.com>
To: Lars-Peter Clausen <lars@metafoo.de>
Cc: Linux MIPS Mailing List <linux-mips@linux-mips.org>,
	David Daney <ddaney.cavm@gmail.com>,
	Linux-sh list <linux-sh@vger.kernel.org>,
	Linus Walleij <linus.walleij@linaro.org>,
	platform-driver-x86@vger.kernel.org,
	"linux-leds@vger.kernel.org" <linux-leds@vger.kernel.org>,
	driverdevel <devel@driverdev.osuosl.org>,
	Alexandre Courbot <gnurou@gmail.com>,
	patches@opensource.wolfsonmicro.com,
	linux-samsungsoc@vger.kernel.org,
	Geert Uytterhoeven <geert@linux-m68k.org>,
	"linux-input@vger.kernel.org" <linux-input@vger.kernel.org>,
	Linux Media Mailing List <linux-media@vger.kernel.org>,
	spear-devel@list.st.com,
	"linux-gpio@vger.kernel.org" <linux-gpio@vger.kernel.org>,
	m@bues.ch,
	"linux-arm-kernel@lists.infradead.org"
	<linux-arm-kernel@lists.infradead.org>,
	"netdev@vger.kernel.org" <netdev@vger.kernel.org>,
	linux-wireless <linux-wireless@vger.kernel.org>,
	linux-kernel@vger.kernel.o
Subject: Re: [PATCH 2/2] gpio: gpiolib: set gpiochip_remove retval to void
Date: Sat, 31 May 2014 15:19:14 +0300	[thread overview]
Message-ID: <20140531121914.GM15585@mwanda> (raw)
In-Reply-To: <5389864B.4000107@metafoo.de>

On Sat, May 31, 2014 at 09:35:39AM +0200, Lars-Peter Clausen wrote:
> On 05/31/2014 01:29 AM, Greg KH wrote:
> >On Fri, May 30, 2014 at 08:16:59PM +0200, Lars-Peter Clausen wrote:
> >>On 05/30/2014 07:33 PM, David Daney wrote:
> >>>On 05/30/2014 04:39 AM, Geert Uytterhoeven wrote:
> >>>>On Fri, May 30, 2014 at 1:30 PM, abdoulaye berthe <berthe.ab@gmail.com>
> >>>>wrote:
> >>>>>--- a/drivers/gpio/gpiolib.c
> >>>>>+++ b/drivers/gpio/gpiolib.c
> >>>>>@@ -1263,10 +1263,9 @@ static void gpiochip_irqchip_remove(struct
> >>>>>gpio_chip *gpiochip);
> >>>>>   *
> >>>>>   * A gpio_chip with any GPIOs still requested may not be removed.
> >>>>>   */
> >>>>>-int gpiochip_remove(struct gpio_chip *chip)
> >>>>>+void gpiochip_remove(struct gpio_chip *chip)
> >>>>>  {
> >>>>>         unsigned long   flags;
> >>>>>-       int             status = 0;
> >>>>>         unsigned        id;
> >>>>>
> >>>>>         acpi_gpiochip_remove(chip);
> >>>>>@@ -1278,24 +1277,15 @@ int gpiochip_remove(struct gpio_chip *chip)
> >>>>>         of_gpiochip_remove(chip);
> >>>>>
> >>>>>         for (id = 0; id < chip->ngpio; id++) {
> >>>>>-               if (test_bit(FLAG_REQUESTED, &chip->desc[id].flags)) {
> >>>>>-                       status = -EBUSY;
> >>>>>-                       break;
> >>>>>-               }
> >>>>>-       }
> >>>>>-       if (status == 0) {
> >>>>>-               for (id = 0; id < chip->ngpio; id++)
> >>>>>-                       chip->desc[id].chip = NULL;
> >>>>>-
> >>>>>-               list_del(&chip->list);
> >>>>>+               if (test_bit(FLAG_REQUESTED, &chip->desc[id].flags))
> >>>>>+                       panic("gpio: removing gpiochip with gpios still
> >>>>>requested\n");
> >>>>
> >>>>panic?
> >>>
> >>>NACK to the patch for this reason.  The strongest thing you should do here
> >>>is WARN.
> >>>
> >>>That said, I am not sure why we need this whole patch set in the first place.
> >>
> >>Well, what currently happens when you remove a device that is a provider of
> >>a gpio_chip which is still in use, is that the kernel crashes. Probably with
> >>a rather cryptic error message. So this patch doesn't really change the
> >>behavior, but makes it more explicit what is actually wrong. And even if you
> >>replace the panic() by a WARN() it will again just crash slightly later.
> >>
> >>This is a design flaw in the GPIO subsystem that needs to be fixed.
> >
> >Then fix the GPIO code properly, don't add a new panic() to the kernel.
> 
> Until somebody comes up with a patch that fixes this for good I
> think that patch is still an improvement over the current situation.
> Rather than keeping the kernel running in a inconsistent state,
> which might cause all kinds of undefined behavior and which will
> lead to a crash eventually, we might as well just crash the kernel
> at the cause of the inconsistent state. This will make it obvious
> why it crashed (compared to a random stacktrace) and will also
> prevent the kernel from running in a undefined state.
> 

Really, adding a panic here is not ok.  With a WARN() then you have
time to save the dmesg to a file.

This CC list is way too huge.  We're all wondering how often this stuff
crashes anyway?  Have you tried to fix the bug instead of just calling
panic()?  Is there a bugzilla entry or something?  Is there a thread on
the list?

Just add a WARN() and fix the bug then cleanup the error handling.

regards,
dan carpenter