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In-Reply-To: <Y+gLd78vChQERZ6A@rowland.harvard.edu>
From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Sat, 11 Feb 2023 13:51:04 -0800
Message-ID: <CAHk-=whXYzkOJZo0xpyYfrhWQg1M7j0OeCojTJ84CN4q9sqb2Q@mail.gmail.com>
Subject: Re: [PATCH RFC] drivers/core: Replace lockdep_set_novalidate_class()
 with unique class keys
To:     Alan Stern <stern@rowland.harvard.edu>, Coly Li <colyli@suse.de>,
        Kent Overstreet <kent.overstreet@gmail.com>
Cc:     Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>,
        syzkaller <syzkaller@googlegroups.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "Rafael J. Wysocki" <rafael@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>,
        Boqun Feng <boqun.feng@gmail.com>,
        LKML <linux-kernel@vger.kernel.org>,
        USB list <linux-usb@vger.kernel.org>,
        Hillf Danton <hdanton@sina.com>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

On Sat, Feb 11, 2023 at 1:41 PM Alan Stern <stern@rowland.harvard.edu> wrote:
>
> @@ -2941,7 +2944,10 @@ void device_initialize(struct device *de
>         kobject_init(&dev->kobj, &device_ktype);
>         INIT_LIST_HEAD(&dev->dma_pools);
>         mutex_init(&dev->mutex);
> -       lockdep_set_novalidate_class(&dev->mutex);
> +       if (!lockdep_static_obj(dev)) {
> +               lockdep_register_key(&dev->mutex_key);
> +               lockdep_set_class(&dev->mutex, &dev->mutex_key);
> +       }
>         spin_lock_init(&dev->devres_lock);
>         INIT_LIST_HEAD(&dev->devres_head);
>         device_pm_init(dev);

So I think this is the right thing to do, but I note that while that
lockdep_set_novalidate_class() was "documented" to only be for
'dev->mutex' by scripts/checkpatch.pl, that horrific thing is also
used by md/bcache/btree.c for the mca_bucket_alloc().

Can we *please* get rid of it there too (it was added by the initial
code, and never had any explicit excuse for it), possibly by using the
same model.

And then we could get rid of lockdep_set_novalidate_class() entirely.
That would be a good thing.

Coly/Kent? See

    https://lore.kernel.org/lkml/Y+gLd78vChQERZ6A@rowland.harvard.edu/

for more context, and

    https://lore.kernel.org/all/28a82f50-39d5-a45f-7c7a-57a66cec0741@I-love.SAKURA.ne.jp/

for some history.

                 Linus