pm24.git/drivers/gpio/gpiolib-cdev.c, branch rust-6.10

gpio: cdev: fix a NULL-pointer dereference with DEBUG enabled

2024-02-16T13:20:07Z

We are actually passing the gc pointer to chip_dbg() so we have to srcu_dereference() it. Fixes: 8574b5b47610 ("gpio: cdev: use correct pointer accessors with SRCU") Reported-by: Marek Szyprowski Closes: https://lore.kernel.org/lkml/179caa10-5f86-4707-8bb0-fe1b316326d6@samsung.com/ Signed-off-by: Bartosz Golaszewski Tested-by: Marek Szyprowski

gpio: cdev: use correct pointer accessors with SRCU

2024-02-15T07:39:18Z

We never dereference the chip pointer in character device code so we can use the lighter rcu_access_pointer() helper. This also makes lockep happier as it no longer complains about suspicious rcu_dereference() usage. Fixes: d83cee3d2bb1 ("gpio: protect the pointer to gpio_chip in gpio_device with SRCU") Reported-by: kernel test robot Closes: https://lore.kernel.org/oe-lkp/202402122234.d85cca9b-lkp@intel.com Signed-off-by: Bartosz Golaszewski Reviewed-by: Linus Walleij Acked-by: Paul E. McKenney

gpio: protect the pointer to gpio_chip in gpio_device with SRCU

2024-02-12T10:00:31Z

Ensure we cannot crash if the GPIO device gets unregistered (and the chip pointer set to NULL) during any of the API calls. To that end: wait for all users of gdev->chip to exit their read-only SRCU critical sections in gpiochip_remove(). For brevity: add a guard class which can be instantiated at the top of every function requiring read-only access to the chip pointer and use it in all API calls taking a GPIO descriptor as argument. In places where we only deal with the GPIO device - use regular guard() helpers and rcu_dereference() for chip access. Do the same in API calls taking a const pointer to gpio_desc. Signed-off-by: Bartosz Golaszewski Reviewed-by: Linus Walleij Acked-by: Andy Shevchenko

gpio: cdev: don't access gdev->chip if it's not needed

2024-02-12T09:51:10Z

The variable holding the number of GPIO lines is duplicated in GPIO device so read it instead of unnecessarily dereferencing the chip pointer. Signed-off-by: Bartosz Golaszewski Reviewed-by: Linus Walleij Acked-by: Andy Shevchenko

gpio: cdev: replace gpiochip_get_desc() with gpio_device_get_desc()

2024-02-12T09:51:03Z

gpio_device_get_desc() is the safer alternative to gpiochip_get_desc(). As we don't really need to dereference the chip pointer to retrieve the descriptors in character device code, let's use it. Signed-off-by: Bartosz Golaszewski Reviewed-by: Linus Walleij Acked-by: Andy Shevchenko

gpio: remove gpio_lock

2024-02-12T09:50:45Z

The "multi-function" gpio_lock is pretty much useless with how it's used in GPIOLIB currently. Because many GPIO API calls can be called from all contexts but may also call into sleeping driver callbacks, there are many places with utterly broken workarounds like yielding the lock to call a possibly sleeping function and then re-acquiring it again without taking into account that the protected state may have changed. It was also used to protect several unrelated things: like individual descriptors AND the GPIO device list. We now serialize access to these two with SRCU and so can finally remove the spinlock. There is of course the question of consistency of lockless access to GPIO descriptors. Because we only support exclusive access to GPIOs (officially anyway, I'm looking at you broken GPIOD_FLAGS_BIT_NONEXCLUSIVE bit...) and the API contract with providers does not guarantee serialization, it's enough to ensure we cannot accidentally dereference an invalid pointer and that the state we present to both users and providers remains consistent. To achieve that: read the flags field atomically except for a few special cases. Read their current value before executing callback code and use this value for any subsequent logic. Modifying the flags depends on the particular use-case and can differ. For instance: when requesting a GPIO, we need to set the REQUESTED bit immediately so that the next user trying to request the same line sees -EBUSY. While at it: the allocations that used GFP_ATOMIC until this point can now switch to GFP_KERNEL. Signed-off-by: Bartosz Golaszewski Reviewed-by: Linus Walleij Acked-by: Andy Shevchenko

gpio: protect the descriptor label with SRCU

2024-02-12T09:50:40Z

In order to ensure that the label is not freed while it's being accessed, let's protect it with SRCU and synchronize it everytime it's changed. Let's modify desc_set_label() to manage the memory used for the label as it can only be freed once synchronize_srcu() returns. Signed-off-by: Bartosz Golaszewski Reviewed-by: Linus Walleij Acked-by: Andy Shevchenko

gpio: provide and use gpiod_get_label()

2024-02-12T09:50:30Z

We will soon serialize access to the descriptor label using SRCU. The write-side of the protection will require calling synchronize_srcu() which must not be called from atomic context. We have two irq helpers: gpiochip_lock_as_irq() and gpiochip_unlock_as_irq() that set the label if the GPIO is not requested but is being used as interrupt. They are called with a spinlock held from the interrupt subsystem. They must not do it if we are to use SRCU so instead let's move the special corner case to a dedicated getter. First: let's implement and use the getter where it's applicable. Signed-off-by: Bartosz Golaszewski Reviewed-by: Linus Walleij Acked-by: Andy Shevchenko

gpio: cdev: remove leftover function pointer typedefs

2024-01-29T10:45:49Z

The locking wrappers were replaces with lock guards. These typedefs are no longer needed. Signed-off-by: Bartosz Golaszewski Reviewed-by: Kent Gibson

gpiolib: cdev: replace locking wrappers for gpio_device with guards

2023-12-27T14:45:45Z

Replace the wrapping functions that inhibit removal of the gpio chip with equivalent guards. Signed-off-by: Kent Gibson Signed-off-by: Bartosz Golaszewski