| Message ID | 20240102155949.73434-1-brgl@bgdev.pl |
|---|---|
| Headers | show |
| Series | gpiolib: use a read-write semaphore to protect the GPIO device list | expand |
On Tue, Jan 2, 2024 at 4:59 PM Bartosz Golaszewski <brgl@bgdev.pl> wrote: > From: Bartosz Golaszewski <bartosz.golaszewski@linaro.org> > > There's time between when we locate the relevant descriptor during > lookup and when we actually take the reference to its parent GPIO > device where - if the GPIO device in question is removed - we'll end up > with a dangling pointer to freed memory. Make sure devices cannot be > removed until we hold a new reference to the device. > > Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org> Also looks right to me! Reviewed-by: Linus Walleij <linus.walleij@linaro.org> Yours, Linus Walleij
On Tue, Jan 2, 2024 at 4:59 PM Bartosz Golaszewski <brgl@bgdev.pl> wrote: > > From: Bartosz Golaszewski <bartosz.golaszewski@linaro.org> > > I'm still figuring out how to keep GPIO descriptors coherent while > (mostly) lockless. In the meantime, I found a potential race-condition > during GPIO descriptor lookup and also figured that the correct way to > protect the GPIO device list is actually a read-write semaphore as we're > not modifying the list very often and readers should be able to iterate > over it concurrently. > > The first patch in this series is new in v2. I realized that we must not > wait until .release() to remove the GPIO device from the list as this is > why pinning down the GPIO device list during lookup would never work - > we always could end up re-taking a reference to an object that was being > released if it got looked up between when the last reference is dropped > and the object is finally removed from the device list. > > v1 -> v2: > - add patch 1/3 to fix a release timing issue > > Bartosz Golaszewski (3): > gpiolib: remove the GPIO device from the list when it's unregistered > gpiolib: replace the GPIO device mutex with a read-write semaphore > gpiolib: pin GPIO devices in place during descriptor lookup > > drivers/gpio/gpiolib-sysfs.c | 2 +- > drivers/gpio/gpiolib.c | 62 ++++++++++++++++++++---------------- > drivers/gpio/gpiolib.h | 2 +- > 3 files changed, 36 insertions(+), 30 deletions(-) > > -- > 2.40.1 > Series applied. Bart
From: Bartosz Golaszewski <bartosz.golaszewski@linaro.org> I'm still figuring out how to keep GPIO descriptors coherent while (mostly) lockless. In the meantime, I found a potential race-condition during GPIO descriptor lookup and also figured that the correct way to protect the GPIO device list is actually a read-write semaphore as we're not modifying the list very often and readers should be able to iterate over it concurrently. The first patch in this series is new in v2. I realized that we must not wait until .release() to remove the GPIO device from the list as this is why pinning down the GPIO device list during lookup would never work - we always could end up re-taking a reference to an object that was being released if it got looked up between when the last reference is dropped and the object is finally removed from the device list. v1 -> v2: - add patch 1/3 to fix a release timing issue Bartosz Golaszewski (3): gpiolib: remove the GPIO device from the list when it's unregistered gpiolib: replace the GPIO device mutex with a read-write semaphore gpiolib: pin GPIO devices in place during descriptor lookup drivers/gpio/gpiolib-sysfs.c | 2 +- drivers/gpio/gpiolib.c | 62 ++++++++++++++++++++---------------- drivers/gpio/gpiolib.h | 2 +- 3 files changed, 36 insertions(+), 30 deletions(-)