linux-kernel - Re: [lockdep] b09be676e0 BUG: unable to handle kernel NULL pointer dereference at 000001f2

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Message-ID: <CA+55aFz2dfH69tUX4GBWmU14=uMseLd_21dAvjohOtJYnfoe7A@mail.gmail.com>
Date:   Tue, 3 Oct 2017 09:57:02 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Fengguang Wu <fengguang.wu@...el.com>
Cc:     Byungchul Park <byungchul.park@....com>,
        Ingo Molnar <mingo@...nel.org>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        LKP <lkp@...org>, Josh Poimboeuf <jpoimboe@...hat.com>
Subject: Re: [lockdep] b09be676e0 BUG: unable to handle kernel NULL pointer
 dereference at 000001f2

On Tue, Oct 3, 2017 at 9:54 AM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> Can we consider just reverting the crossrelease thing?
>
> The apparent stack corruption really worries me [...]

Side note: I also think the thing is just broken.

Any actual cross-releaser should be way more annotated than just "set
cross to 1" in the lockdep map.

The place where the release is done should simply be special.

Because we should *not* encourage the whole "acquire by one context,
release by another" as being something normal and "just set the flag
to let lockdep know".

So that commit is apparently buggy, but I think it might be more
fundamentally the wrong model too.

               Linus