| Message ID | 1401449454-30895-2-git-send-email-berthe.ab@gmail.com (mailing list archive) |
|---|---|
| State | Awaiting Upstream |
| Headers | show |
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? Is this likely to happen? Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds -- To unsubscribe from this list: send the line "unsubscribe linux-sh" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Fri, May 30, 2014 at 01:39:15PM +0200, Geert Uytterhoeven wrote: > > + if (test_bit(FLAG_REQUESTED, &chip->desc[id].flags)) > > + panic("gpio: removing gpiochip with gpios still requested\n"); > > panic? > > Is this likely to happen? And while we're at it - panic() is going to add a \n itself so don't pass a string ending in \n to panic(). Ralf -- To unsubscribe from this list: send the line "unsubscribe linux-sh" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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. David Daney > > Is this likely to happen? > > Gr{oetje,eeting}s, > > Geert > > -- > Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org > > In personal conversations with technical people, I call myself a hacker. But > when I'm talking to journalists I just say "programmer" or something like that. > -- Linus Torvalds > > -- To unsubscribe from this list: send the line "unsubscribe linux-sh" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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. - Lars -- To unsubscribe from this list: send the line "unsubscribe linux-sh" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 06/09/2014 01:29 PM, Lars-Peter Clausen wrote: > On 06/09/2014 01:18 AM, Ben Dooks 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. >> >> Surely then the best way is to error out to the module unload and >> stop the driver being unloaded? >> > > You can't error out on module unload, although that's not really relevant > here. gpiochip_remove() is typically called when the device that registered > the GPIO chip is unbound. And despite some remove() callbacks having a > return type of int you can not abort the removal of a device. It is a design flaw in many subsystems having providers and consumers, not only GPIO. The same situation is with clock providers, regulators, phys, drm_panels, ..., at least it was such last time I have tested it. The problem is that many frameworks assumes that lifetime of provider is always bigger than lifetime of its consumers, and this is wrong assumption - usually it is not possible to prevent unbinding driver from device, so if the device is a provider there is no way to inform consumers about his removal. Some solution for such problems is to use some kind of availability callbacks for requesting resources (gpios, clocks, regulators,...) instead of simple 'getters' (clk_get, gpiod_get). Callbacks should guarantee that the resource is always valid between callback reporting its availability and callback reporting its removal. Such approach seems to be complicated at the first sight but it should allow to make the code safe and as a bonus it will allow to avoid deferred probing. Btw I have send already RFC for such framework [1]. [1]: https://lkml.org/lkml/2014/4/30/345 Regards Andrzej > > - Lars > -- To unsubscribe from this list: send the line "unsubscribe linux-sh" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 06/09/2014 03:43 PM, David Laight wrote: > From: Of Andrzej Hajda > ... >>> You can't error out on module unload, although that's not really relevant >>> here. gpiochip_remove() is typically called when the device that registered >>> the GPIO chip is unbound. And despite some remove() callbacks having a >>> return type of int you can not abort the removal of a device. >> >> It is a design flaw in many subsystems having providers and consumers, >> not only GPIO. The same situation is with clock providers, regulators, >> phys, drm_panels, ..., at least it was such last time I have tested it. >> >> The problem is that many frameworks assumes that lifetime of provider is >> always bigger than lifetime of its consumers, and this is wrong >> assumption - usually it is not possible to prevent unbinding driver from >> device, so if the device is a provider there is no way to inform >> consumers about his removal. >> >> Some solution for such problems is to use some kind of availability >> callbacks for requesting resources (gpios, clocks, regulators,...) >> instead of simple 'getters' (clk_get, gpiod_get). Callbacks should >> guarantee that the resource is always valid between callback reporting >> its availability and callback reporting its removal. Such approach seems >> to be complicated at the first sight but it should allow to make the >> code safe and as a bonus it will allow to avoid deferred probing. >> Btw I have send already RFC for such framework [1]. > > Callbacks for delete are generally a locking nightmare. > A two-way handshake is also usually needed to avoid problems > with concurrent disconnect requests. The framework I have proposed is lock-less[1] and concurrent requests are serialized so both objections are invalid. [1]: in fact the framework uses spinlock, but only to protect internal list simple operations, and even this could be converted to fully lock-less implementation. Andrzej > > David > -- To unsubscribe from this list: send the line "unsubscribe linux-sh" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c index f48817d..022543f 100644 --- 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"); } + for (id = 0; id < chip->ngpio; id++) + chip->desc[id].chip = NULL; + list_del(&chip->list); spin_unlock_irqrestore(&gpio_lock, flags); - - if (status == 0) - gpiochip_unexport(chip); - - return status; + gpiochip_unexport(chip); } EXPORT_SYMBOL_GPL(gpiochip_remove); diff --git a/include/linux/gpio/driver.h b/include/linux/gpio/driver.h index 1827b43..72ed256 100644 --- a/include/linux/gpio/driver.h +++ b/include/linux/gpio/driver.h @@ -138,7 +138,7 @@ extern const char *gpiochip_is_requested(struct gpio_chip *chip, /* add/remove chips */ extern int gpiochip_add(struct gpio_chip *chip); -extern int __must_check gpiochip_remove(struct gpio_chip *chip); +void gpiochip_remove(struct gpio_chip *chip); extern struct gpio_chip *gpiochip_find(void *data, int (*match)(struct gpio_chip *chip, void *data));
This avoids handling gpiochip remove error in device remove handler. Signed-off-by: abdoulaye berthe <berthe.ab@gmail.com> --- drivers/gpio/gpiolib.c | 24 +++++++----------------- include/linux/gpio/driver.h | 2 +- 2 files changed, 8 insertions(+), 18 deletions(-)