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Message-ID: <CAMRc=MdER_JNcvPMRuzbDFpAUqarC9K8KRP+i5SFTW3H7Mkg=w@mail.gmail.com>
Date: Thu, 24 Oct 2024 08:15:31 +0000
From: Bartosz Golaszewski <brgl@...ev.pl>
To: Mark Brown <broonie@...nel.org>
Cc: Linus Walleij <linus.walleij@...aro.org>, Kent Gibson <warthog618@...il.com>,
linux-gpio@...r.kernel.org, linux-kernel@...r.kernel.org,
Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
Subject: Re: [PATCH v5 8/8] gpiolib: notify user-space about in-kernel line
state changes
On Thu, 24 Oct 2024 08:49:30 +0200, Bartosz Golaszewski <brgl@...ev.pl> said:
> On Wed, Oct 23, 2024 at 11:05 PM Mark Brown <broonie@...nel.org> wrote:
>>
>> On Fri, Oct 18, 2024 at 11:10:16AM +0200, Bartosz Golaszewski wrote:
>> > From: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
>> >
>> > We currently only notify user-space about line config changes that are
>> > made from user-space. Any kernel config changes are not signalled.
>> >
>> > Let's improve the situation by emitting the events closer to the source.
>> > To that end let's call the relevant notifier chain from the functions
>> > setting direction, gpiod_set_config(), gpiod_set_consumer_name() and
>> > gpiod_toggle_active_low(). This covers all the options that we can
>> > inform the user-space about. We ignore events which don't have
>> > corresponding flags exported to user-space on purpose - otherwise the
>> > user would see a config-changed event but the associated line-info would
>> > remain unchanged.
>>
>> Today's -next is not booting on several of my platforms, including
>> beaglebone-black, i.MX8MP-EVK and pine64plus. Bisects are pointing at
>> this commit, and i.MX8MP-EVK is actually giving some console output:
>>
>> [ 2.502208] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000000
>> [ 2.511036] Mem abort info:
>>
>> ...
>>
>> [ 2.679934] Call trace:
>> [ 2.682379] gpiod_direction_output+0x34/0x5c
>> [ 2.686745] i2c_register_adapter+0x59c/0x670
>> [ 2.691111] __i2c_add_numbered_adapter+0x58/0xa8
>> [ 2.695822] i2c_add_adapter+0xa0/0xd0
>> [ 2.699578] i2c_add_numbered_adapter+0x2c/0x38
>> [ 2.704117] i2c_imx_probe+0x2d0/0x640
>>
>> which looks plausible given the change.
>>
>> Full boot log for i.MX8MP-EVK:
>>
>> https://lava.sirena.org.uk/scheduler/job/887083
>>
>> Bisect log for that, the others look similar (the long run of good/bad
>> tags at the start for random commits is my automation pulling test
>> results it already knows about in the affected range to try to speed up
>> the bisect):
>>
>
> Hi Mark!
>
> Any chance you could post the output of
>
> scripts/faddr2line drivers/gpio/gpiolib.o gpiod_direction_output+0x34/0x5c
>
> for that build?
>
> Bart
>
While I can't really reproduce it, I've looked at what could be wrong and
figured that the NULL-pointer in question can possibly be the
line_state_notifier.
I realized that for some historical reasons we add the GPIO device to the
global list before it's fully set up - including initializing the notifier.
In some corner cases (devlinks borked?) this could lead to consumers requesting
GPIOs before their provider is ready.
Mark: could you try the following diff and let me know if it works?
diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index ae758ba6dc3d..4258acac0162 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -987,45 +987,6 @@ int gpiochip_add_data_with_key(struct gpio_chip
*gc, void *data,
gdev->ngpio = gc->ngpio;
gdev->can_sleep = gc->can_sleep;
-
- scoped_guard(mutex, &gpio_devices_lock) {
- /*
- * TODO: this allocates a Linux GPIO number base in the global
- * GPIO numberspace for this chip. In the long run we want to
- * get *rid* of this numberspace and use only descriptors, but
- * it may be a pipe dream. It will not happen before we get rid
- * of the sysfs interface anyways.
- */
- base = gc->base;
- if (base < 0) {
- base = gpiochip_find_base_unlocked(gc->ngpio);
- if (base < 0) {
- ret = base;
- base = 0;
- goto err_free_label;
- }
-
- /*
- * TODO: it should not be necessary to reflect the
- * assigned base outside of the GPIO subsystem. Go over
- * drivers and see if anyone makes use of this, else
- * drop this and assign a poison instead.
- */
- gc->base = base;
- } else {
- dev_warn(&gdev->dev,
- "Static allocation of GPIO base is deprecated, use dynamic
allocation.\n");
- }
-
- gdev->base = base;
-
- ret = gpiodev_add_to_list_unlocked(gdev);
- if (ret) {
- chip_err(gc, "GPIO integer space overlap, cannot add chip\n");
- goto err_free_label;
- }
- }
-
ATOMIC_INIT_NOTIFIER_HEAD(&gdev->line_state_notifier);
BLOCKING_INIT_NOTIFIER_HEAD(&gdev->device_notifier);
@@ -1103,6 +1064,45 @@ int gpiochip_add_data_with_key(struct gpio_chip
*gc, void *data,
if (ret)
goto err_remove_irqchip;
}
+
+ scoped_guard(mutex, &gpio_devices_lock) {
+ /*
+ * TODO: this allocates a Linux GPIO number base in the global
+ * GPIO numberspace for this chip. In the long run we want to
+ * get *rid* of this numberspace and use only descriptors, but
+ * it may be a pipe dream. It will not happen before we get rid
+ * of the sysfs interface anyways.
+ */
+ base = gc->base;
+ if (base < 0) {
+ base = gpiochip_find_base_unlocked(gc->ngpio);
+ if (base < 0) {
+ ret = base;
+ base = 0;
+ goto err_free_label;
+ }
+
+ /*
+ * TODO: it should not be necessary to reflect the
+ * assigned base outside of the GPIO subsystem. Go over
+ * drivers and see if anyone makes use of this, else
+ * drop this and assign a poison instead.
+ */
+ gc->base = base;
+ } else {
+ dev_warn(&gdev->dev,
+ "Static allocation of GPIO base is deprecated, use dynamic
allocation.\n");
+ }
+
+ gdev->base = base;
+
+ ret = gpiodev_add_to_list_unlocked(gdev);
+ if (ret) {
+ chip_err(gc, "GPIO integer space overlap, cannot add chip\n");
+ goto err_free_label;
+ }
+ }
+
return 0;
err_remove_irqchip:
Thanks
Bartosz
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