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From:   Pintu Agarwal <pintu.ping@gmail.com>
Date:   Fri, 12 Nov 2021 12:48:55 +0530
Message-ID: <CAOuPNLg_YwyhK6iPZZbRWe57Kkr1d8LjJaDniCvvOqk4t2-Sog@mail.gmail.com>
Subject: Re: Kernel-4.14: With ubuntu-18.04 building rootfs images and booting
 gives SQUASHFS error: xz decompression failed, data probably corrupt
To:     open list <linux-kernel@vger.kernel.org>,
        linux-mtd <linux-mtd@lists.infradead.org>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        dm-devel@redhat.com, Phillip Lougher <phillip@squashfs.org.uk>,
        Mikulas Patocka <mpatocka@redhat.com>,
        Richard Weinberger <richard@nod.at>,
        Florian Fainelli <f.fainelli@gmail.com>,
        Sumit Semwal <sumit.semwal@linaro.org>,
        Thomas Petazzoni <thomas.petazzoni@bootlin.com>,
        drosen@google.com, astrachan@google.com, speed.eom@samsung.com,
        Sami Tolvanen <samitolvanen@google.com>, snitzer@redhat.com
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Hi,

On Tue, 9 Nov 2021 at 21:04, Pintu Agarwal <pintu.ping@gmail.com> wrote:

> > > We only get these squashfs errors flooded in the boot logs:
> > > {{{
> > > ....
> > > [    5.153479] device-mapper: init: dm-0 is ready
> > > [    5.334282] VFS: Mounted root (squashfs filesystem) readonly on device 253:0.
> > > ....
> > > [    8.954120] SQUASHFS error: xz decompression failed, data probably corrupt
> > > [    8.954153] SQUASHFS error: squashfs_read_data failed to read block 0x1106
> > > [    8.970316] SQUASHFS error: Unable to read data cache entry [1106]
> > > [    8.970349] SQUASHFS error: Unable to read page, block 1106, size 776c
> > > [    8.980298] SQUASHFS error: Unable to read data cache entry [1106]
> > > [    8.981911] SQUASHFS error: Unable to read page, block 1106, size 776c
> > > [    8.988280] SQUASHFS error: Unable to read data cache entry [1106]
> > > ....
> > > }}}
> > >

One more observation:
When I disable FEC flag in bootloader, I see the below error:
[    8.360791] device-mapper: verity: 253:0: data block 2 is corrupted
[    8.361134] device-mapper: verity: 253:0: data block 3 is corrupted
[    8.366016] SQUASHFS error: squashfs_read_data failed to read block 0x1106
[    8.379652] SQUASHFS error: Unable to read data cache entry [1106]
[    8.379680] SQUASHFS error: Unable to read page, block 1106, size 7770

Also, now I see that the decompress error is gone, but the read error
is still there.

This seems to me that dm-verity detects some corrupted blocks but with
FEC it auto corrects itself, how when dm-verity auto corrects itself,
the squashfs decompression algorithm somehow could not understand it.

So, it seems like there is some mis-match between the way FEC
correction and the squashfs decompression happens ?

Is this issue seen by anybody else here ?


Thanks,
Pintu