linux-kernel - Re: [PATCH] gpio: gpiolib-cdev: Fix potential &lr->wait.lock deadlock issue

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Date:   Mon, 26 Jun 2023 09:53:49 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     YE Chengfeng <cyeaa@...nect.ust.hk>
Cc:     "linus.walleij@...aro.org" <linus.walleij@...aro.org>,
        "brgl@...ev.pl" <brgl@...ev.pl>,
        "andy@...nel.org" <andy@...nel.org>,
        "linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] gpio: gpiolib-cdev: Fix potential &lr->wait.lock deadlock issue

On Sun, Jun 25, 2023 at 5:45 PM YE Chengfeng <cyeaa@...nect.ust.hk> wrote:
>
> linereq_put_event is called from both interrupt context (e.g.,
> edge_irq_thread) and process context (process_hw_ts_thread).
> Therefore, interrupt should be disabled before acquiring lock
> &lr->wait.lock inside linereq_put_event to avoid deadlock when
> the lock is held in process context and edge_irq_thread comes.
>
> Similarly, linereq_read_unlocked running in process context
> also acquies the same lock. It also need to disable interrupt

acquires

> otherwise deadlock could happen if the irq edge_irq_thread
> comes to execution while the lock is held.
>
> Fix the two potential deadlock issues by spin_lock_irqsave.

Sounds legit to me, but
1) do you have any warning/oops/etc to show the real case?
2) shouldn't we annotate with respective lockdep asserts this code?

-- 
With Best Regards,
Andy Shevchenko