linux-kernel - Re: BUG: unable to handle kernel NULL pointer dereference at 00000000000000a8 in nilfs_segctor_do

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Date:   Sun, 16 Feb 2020 12:59:59 +0900
From:   Ryusuke Konishi <konishi.ryusuke@...il.com>
To:     ARAI Shun-ichi <hermes@...es.dti.ne.jp>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        linux-nilfs <linux-nilfs@...r.kernel.org>,
        "Brian G." <gissf1@...il.com>
Subject: Re: BUG: unable to handle kernel NULL pointer dereference at
 00000000000000a8 in nilfs_segctor_do_construct

Thank you Arai-san,

Your method with loopback device worked to reproduce the issue
even where the bug doesn't easily hit for physical devices.

Regards,
Ryusuke Konishi

On Sun, Feb 16, 2020 at 11:11 AM ARAI Shun-ichi <hermes@...es.dti.ne.jp> wrote:
>
> And,
>
> In <20200210.224609.499887311281343618.hermes@...es.dti.ne.jp>;
>    ARAI Shun-ichi <hermes@...es.dti.ne.jp> wrote
>    as Subject "Re: BUG: unable to handle kernel NULL pointer dereference at 00000000000000a8 in nilfs_segctor_do_construct":
>
> > Hi,
> >
> > FYI, reporting additional test results.
> >
> > I reproduced this problem with clean NILFS2 fs in previous mail.
> > "clean" means that "make filesystem before every tests."
> > In this mail, I tried to reproduct with/without VG/LV, LUKS, loopback.
> >
> > * Not reproduced
> >  USB stick - primary partition - NILFS2
> >  USB stick - primary partition - VG/LV - NILFS2
> >  USB stick - primary partition - VG/LV - LUKS - NILFS2
> >  USB stick - primary partition - LUKS - VG/LV - NILFS2
> >  USB stick - primary partition - LUKS - VG/LV - LUKS - NILFS2
> >  /tmp (tmpfs) - regular file - NILFS2 (loopback mount, kernel 4.19.82)
> >  USB stick - primary partition(512MiB) - NILFS2
> >
> > * Reproduced (always, immediately)
> >  /tmp (tmpfs) - regular file - NILFS2 (loopback mount)
> >  USB stick - primary partition - ext4 - regular file - NILFS2 (loopback mount)
>
> this loopback problem is seen in Kernel 5.5.4.
>
> > Test conditions:
> >  kernel 4.19.86 (same as previous test)
> >  NILFS2/ext4 filesystem, VG/LV, LUKS were made with default parameters
> >  size of "primary partition" in USB stick is approx. 14GiB
> >  size of "regular file" is approx. 512MiB
> >  "reproduce": mount NILFS2, touch file, sync