linux-kernel - Re: [PATCH 0/2] gpio: shared: another set of small fixes

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <CAMRc=Mc0YUvoEYB7RCEBWmU1gM_zEzB0mhQ3D9+fO7jwkmAtGQ@mail.gmail.com>
Date: Mon, 5 Jan 2026 09:42:35 -0800
From: Bartosz Golaszewski <brgl@...nel.org>
To: Marek Szyprowski <m.szyprowski@...sung.com>
Cc: Bartosz Golaszewski <bartosz.golaszewski@....qualcomm.com>, Linus Walleij <linusw@...nel.org>, 
	linux-gpio@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Bartosz Golaszewski <brgl@...nel.org>
Subject: Re: [PATCH 0/2] gpio: shared: another set of small fixes

On Mon, 5 Jan 2026 18:22:31 +0100, Marek Szyprowski
<m.szyprowski@...sung.com> said:
> On 05.01.2026 17:53, Bartosz Golaszewski wrote:
>> On Mon, 5 Jan 2026 17:48:05 +0100, Marek Szyprowski
>> <m.szyprowski@...sung.com> said:
>>> On 05.01.2026 16:52, Bartosz Golaszewski wrote:
>>>> Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@....qualcomm.com>
>>>> ---
>>>> Bartosz Golaszewski (2):
>>>>         gpio: shared: assign the correct firmware node for reset-gpio use-case
>>>>         gpio: shared: fix a race condition
>>>>
>>>>    drivers/gpio/gpiolib-shared.c | 4 +++-
>>>>    1 file changed, 3 insertions(+), 1 deletion(-)
>>>> ---
>>>> base-commit: 19fb766a1e5ed5943a62fc671c09d45352a81b1d
>>>> change-id: 20260105-gpio-shared-fixes-40a8ec3b6b25
>>> Those patches indeed fixes some timing issues with the commit
>>> 49416483a953 ("gpio: shared: allow sharing a reset-gpios pin between
>>> reset-gpio and gpiolib"), but they also reveals another one. I've
>>> initially thought that this is a false positive and needs only a proper
>>> lockdep annotation, but some boards hang just after similar lockdep splat:
>>>
>>> ============================================
>>> WARNING: possible recursive locking detected
>>> 6.19.0-rc4-next-20260105+ #11974 Not tainted
>>> --------------------------------------------
>>> (udev-worker)/192 is trying to acquire lock:
>>> ffff000004c15098 (&ref->lock){+.+.}-{4:4}, at:
>>> gpio_shared_dev_is_reset_gpio+0xcc/0x234
>>>
>>> but task is already holding lock:
>>> ffff000004c15898 (&ref->lock){+.+.}-{4:4}, at:
>>> gpio_shared_add_proxy_lookup+0x98/0x228
>>>
>>> other info that might help us debug this:
>>>    Possible unsafe locking scenario:
>>>
>>>          CPU0
>>>          ----
>>>     lock(&ref->lock);
>>>     lock(&ref->lock);
>>>
>>>    *** DEADLOCK ***
>>>
>>>    May be due to missing lock nesting notation
>>>
>>> 3 locks held by (udev-worker)/192:
>>>    #0: ffff00000b3ad8e8 (&dev->mutex){....}-{4:4}, at:
>>> __driver_attach+0x90/0x1ac
>>>    #1: ffff8000830f2600 (gpio_devices_srcu){.+.+}-{0:0}, at:
>>> gpiod_find_and_request+0x0/0x574
>>>    #2: ffff000004c15898 (&ref->lock){+.+.}-{4:4}, at:
>>> gpio_shared_add_proxy_lookup+0x98/0x228
>>>
>> Ah this must be due to also trying to compare the ref to the base ref...
>>
>> Could you try to add the following on top:
>>
>> diff --git a/drivers/gpio/gpiolib-shared.c b/drivers/gpio/gpiolib-shared.c
>> index 198951c4c80b..5f3b8bc4a4fc 100644
>> --- a/drivers/gpio/gpiolib-shared.c
>> +++ b/drivers/gpio/gpiolib-shared.c
>> @@ -378,6 +378,9 @@ static bool gpio_shared_dev_is_reset_gpio(struct
>> device *consumer,
>>   	 * arguments match the ones from this consumer's node.
>>   	 */
>>   	list_for_each_entry(real_ref, &entry->refs, list) {
>> +		if (real_ref == ref)
>> +			continue;
>> +
>>   		guard(mutex)(&real_ref->lock);
>>
>>   		if (!real_ref->fwnode)
>>
>>
>> If that works, I'll send a v2.
>
> This fixed the hangs, but the lockdep whining is still there.
>

Then it's a false-positive. I will try to play with lockdep_set_class()
tomorrow.

Bart