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

From: Minchan Kim <minchan@kernel.org>
To: Sergey Senozhatsky <senozhatsky@chromium.org>,
	umgwanakikbuti@gmail.com, bigeasy@linutronix.de
Cc: Naresh Kamboju <naresh.kamboju@linaro.org>,
	open list <linux-kernel@vger.kernel.org>,
	linux-fsdevel@vger.kernel.org,
	Linux ARM <linux-arm-kernel@lists.infradead.org>,
	"open list:KERNEL SELFTEST FRAMEWORK" 
	<linux-kselftest@vger.kernel.org>,
	linux-block <linux-block@vger.kernel.org>,
	regressions@lists.linux.dev, Jens Axboe <axboe@kernel.dk>,
	Nitin Gupta <ngupta@vflare.org>
Subject: Re: qemu-arm: zram: mkfs.ext4 : Unable to handle kernel NULL pointer dereference at virtual address 00000140
Date: Mon, 13 Jun 2022 09:49:03 -0700	[thread overview]
Message-ID: <Yqdqfz4Ycbg33k1R@google.com> (raw)
In-Reply-To: <YqbtH9F47dkZghJ7@google.com>

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/