linux-kernel - Re: qemu-arm: zram: mkfs.ext4 : Unable to handle kernel NULL pointer dereference at virtual address 00000140

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Date:   Mon, 13 Jun 2022 09:49:03 -0700
From:   Minchan Kim <minchan@...nel.org>
To:     Sergey Senozhatsky <senozhatsky@...omium.org>,
        umgwanakikbuti@...il.com, bigeasy@...utronix.de
Cc:     Naresh Kamboju <naresh.kamboju@...aro.org>,
        open list <linux-kernel@...r.kernel.org>,
        linux-fsdevel@...r.kernel.org,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>,
        linux-block <linux-block@...r.kernel.org>,
        regressions@...ts.linux.dev, Jens Axboe <axboe@...nel.dk>,
        Nitin Gupta <ngupta@...are.org>
Subject: Re: qemu-arm: zram: mkfs.ext4 : Unable to handle kernel NULL pointer
 dereference at virtual address 00000140

On Mon, Jun 13, 2022 at 04:54:07PM +0900, Sergey Senozhatsky wrote:
> Hello,
> 
> On (22/06/12 20:56), Naresh Kamboju wrote:
> > 
> > I have tested this patch and the reported issue got resolved [1].
> >
> 
> Many thanks for the tests.
> 
> Quite honestly I was hoping that the patch would not help :) Well, ok,
> we now know that it's mapping area lock and the lockdep part of its
> memory is zero-ed out. The question is - "why?" It really should not
> be zeroed out.

Ccing Mike and Sebastian who are author/expert of the culprit patch

Naresh found zsmalloc crashed on the testing [1] and confirmed
that Sergey's patch[2] fixed the problem.
However, I don't understand why we need reinit the local_lock
on cpu_up handler[3].

Could you guys shed some light?

[1] https://lore.kernel.org/all/CA+G9fYtVOfWWpx96fa3zzKzBPKiNu1w3FOD4j++G8MOG3Vs0EA@mail.gmail.com/
[2] https://lore.kernel.org/all/YqBRZcsfrRMZXMCC@google.com/
[3] https://lore.kernel.org/all/YqEKapKLBgKEXGBg@google.com/