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Date:   Wed, 8 Jun 2022 11:39:52 +0900
From:   Sergey Senozhatsky <senozhatsky@chromium.org>
To:     Minchan Kim <minchan@kernel.org>
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>,
        Sergey Senozhatsky <senozhatsky@chromium.org>,
        Nitin Gupta <ngupta@vflare.org>
Subject: Re: qemu-arm: zram: mkfs.ext4 : Unable to handle kernel NULL pointer
 dereference at virtual address 00000140
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On (22/06/07 16:52), Minchan Kim wrote:
> > rootfs: https://oebuilds.tuxbuild.com/29zhlbEc3EWq2wod9Uy964Bp27q/images/am57xx-evm/rpb-console-image-lkft-am57xx-evm-20220601222434.rootfs.ext4.gz
> > kernel: https://builds.tuxbuild.com/29zhqJJizU2Y7Ka7ArhryUOrNDC/zImage
> > 
> > Boot command,
> >  /usr/bin/qemu-system-aarch64 -cpu host,aarch64=off -machine
> > virt-2.10,accel=kvm -nographic -net
> > nic,model=virtio,maaacaddr=BA:DD:AD:CC:09:04 -net tap -m 2048 -monitor
> > none -kernel kernel/zImage --append "console=ttyAMA0 root=/dev/vda rw"
> > -hda rootfs/rpb-console-image-lkft-am57xx-evm-20220601222434.rootfs.ext4
> > -m 4096 -smp 2
> > 
> > # cd /opt/kselftests/default-in-kernel/zram
> > # ./zram.sh
> > 
> > Allow me sometime I will try to bisect this problem.
> 
> Thanks for sharing the info. 
> 
> I managed to work your rootfs with my local arm build
> based on the problematic git tip. 
> However, I couldn't suceed to reproduce it.
> 
> I needed to build zsmalloc/zram built-in instead of modules
> Is it related? Hmm,
> 
> Yeah, It would be very helpful if you could help to bisect it.

This looks like a NULL lock->name dereference in lockdep. I suspect
that somehow local_lock doesn't get .dep_map initialized. Maybe running
the kernel with CONFIG_DEBUG_LOCK_ALLOC would help us? Naresh, can you
help us with this?