linux-kernel - Re: lockdep: incorrect deadlock warning with two GPIO expanders

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Message-ID: <CAMpxmJXJexFWXX2nBfLr6Uy+8WXmEeChOgwq=aDSqGzxAmeZ=Q@mail.gmail.com>
Date:   Thu, 15 Sep 2016 17:23:06 +0200
From:   Bartosz Golaszewski <bgolaszewski@...libre.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        Alexandre Courbot <gnurou@...il.com>,
        Ingo Molnar <mingo@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-gpio <linux-gpio@...r.kernel.org>
Subject: Re: lockdep: incorrect deadlock warning with two GPIO expanders

2016-09-15 16:38 GMT+02:00 Peter Zijlstra <peterz@...radead.org>:
> On Thu, Sep 15, 2016 at 04:08:52PM +0200, Bartosz Golaszewski wrote:
>> 2016-09-15 15:39 GMT+02:00 Peter Zijlstra <peterz@...radead.org>:
>
>> > In any case, if this fails, we can always punt and simply count the
>> > total number of instances of this driver on the system and go with that.
>> >
>>
>> But for __mutex_init() to work with the key argument you need to know
>> it at compile time, right?
>
> You can do something like:
>
>         mutex_init(&mutex);
>         lockdep_set_subclass(&mutex, nr);
>
> which will of course fail at runtime the moment nr >= 8, but is that
> really a concern?
>
> Equally you can do:
>
> static struct lock_class_key my_keys[NR];
>
>         mutex_init(&mutex);
>         BUG_ON(nr > NR);
>         lockdep_set_class(&mutex, my_keys + nr);
>
> and have a bigger limit.

Thanks, I was not aware of this API.

Best regards,
Bartosz Golaszewski