Messages in this thread | | | Subject | Re: [PATCH v4] gpio: Return EPROBE_DEFER if gc->to_irq is NULL | From | Shreeya Patel <> | Date | Fri, 11 Feb 2022 15:33:44 +0530 |
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On 11/02/22 6:56 am, Gabriel Krisman Bertazi wrote: > Bartosz Golaszewski <brgl@bgdev.pl> writes: > >> My email address changed in September, that's why I didn't see the >> email you sent in November to my old one. > Hi Bart, > > thanks for the prompt reply and sorry for the wrong email address. > >> gpiod_to_irq() can be used in context other than driver probing, I'm >> worried existing users would not know how to handle it. Also: how come >> you can get the GPIO descriptor from the provider but its interrupts >> are not yet set up? > I'm definitely some context here, as its been quite a while. > Shreeya, feel free to pitch in. :)
Existing users will probably receive -ENXIO in case to_irq is not set and wasn't intended to be set. We are trying to solve the race which happens frequently in cases where I2C is set as built-in and pinctrl-amd is set as module. There is no dependency between I2C and pinctrl-amd, while pinctrl-amd is still trying to set the gc irq members through gpiochip_add_irqchip, I2C calls gpiod_to_irq() which leads to returning -ENXIO since gc->to_irq is still NULL
There have also been cases where gc->to_irq is set successfully but other members are yet to be initalized by gpiochip_add_irqchip like the domain variable which is being used in .to_irq() and ultimately leads to a NULL pointer dereference as Gabriel mentioned. I am working on a fix which would use mutex to not let gc irq members be accessed until they all have been completely initialized.
I2C calls gpiod_to_irq through the following stack trace
kernel: Call Trace: kernel: gpiod_to_irq.cold+0x49/0x8f kernel: acpi_dev_gpio_irq_get_by+0x113/0x1f0 kernel: i2c_acpi_get_irq+0xc0/0xd0 kernel: i2c_device_probe+0x28a/0x2a0 kernel: really_probe+0xf2/0x460 kernel: driver_probe_device+0xe8/0x160
and pinctrl-amd makes gc visible through gpiochip_add_data_with_key()
Thanks, Shreeya Patel
> This is one of the races we saw in gpiochip_add_irqchip, depending on > the probe order. The gc is already visible while partially initialized, > if pinctrl-amd hasn't been probed yet. Another device being probed can > hit an -ENXIO here if to_irq is yet uninitialized or enter .to_irq() and > oops. Shreeya's patch workarounds the first issue, but is not a > solution for the second. > > There is another patch that has been flying around to address the Oops. > > https://lkml.org/lkml/2021/11/8/900 > > She's been working on a proper solution for that one, which might > actually address this too and replace the current patch. Maybe you > could help us get to a proper solution there? I'm quite unfamiliar with > this code myself :) >
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