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

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Message-ID: <YqAMmTiwcyS3Ttla@google.com>
Date:   Wed, 8 Jun 2022 11:42:33 +0900
From:   Sergey Senozhatsky <senozhatsky@...omium.org>
To:     Minchan Kim <minchan@...nel.org>
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>,
        Sergey Senozhatsky <senozhatsky@...omium.org>
Subject: Re: qemu-arm: zram: mkfs.ext4 : Unable to handle kernel NULL pointer
 dereference at virtual address 00000140

On (22/06/08 11:39), Sergey Senozhatsky wrote:
> 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?

Hmm, actually, hold on. mapping_area is per-CPU, so what happens if CPU
get offlined and onlined again? I don't see us re-initializing mapping_area
local_lock_init(&zs_map_area.lock) and so on.