Messages in this thread | | | From | Bartosz Golaszewski <> | Date | Mon, 28 Nov 2022 22:36:09 +0100 | Subject | Re: [PATCH v2 2/2] gpiolib: protect the GPIO device against being dropped while in use by user-space |
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On Mon, Nov 28, 2022 at 8:21 PM Andy Shevchenko <andriy.shevchenko@linux.intel.com> wrote: > > On Mon, Nov 28, 2022 at 06:52:14PM +0100, Bartosz Golaszewski wrote: > > From: Bartosz Golaszewski <bartosz.golaszewski@linaro.org> > > > > While any of the GPIO cdev syscalls is in progress, the kernel can call > > gpiochip_remove() (for instance, when a USB GPIO expander is disconnected) > > which will set gdev->chip to NULL after which any subsequent access will > > cause a crash. > > > > To avoid that: use an RW-semaphore in which the syscalls take it for > > reading (so that we don't needlessly prohibit the user-space from calling > > syscalls simultaneously) while gpiochip_remove() takes it for writing so > > that it can only happen once all syscalls return. > > Missed also Dependency (the previous change). > > > Fixes: d7c51b47ac11 ("gpio: userspace ABI for reading/writing GPIO lines") > > Fixes: 3c0d9c635ae2 ("gpiolib: cdev: support GPIO_V2_GET_LINE_IOCTL and GPIO_V2_LINE_GET_VALUES_IOCTL") > > Fixes: aad955842d1c ("gpiolib: cdev: support GPIO_V2_GET_LINEINFO_IOCTL and GPIO_V2_GET_LINEINFO_WATCH_IOCTL") > > Fixes: a54756cb24ea ("gpiolib: cdev: support GPIO_V2_LINE_SET_CONFIG_IOCTL") > > Fixes: 7b8e00d98168 ("gpiolib: cdev: support GPIO_V2_LINE_SET_VALUES_IOCTL") > > ... > > > + down_read(&gdev->sem); > > > > - if (!gdev->chip) > > + if (!gdev->chip) { > > + up_read(&gdev->sem); > > return -ENODEV; > > + } > > Wouldn't be easier to wrap existing functions (with their renaming) into a new > ones with semaphore? >
You're probably right, it would be much cleaner. I'll see about it.
Bart
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