[Bug 215712] New: kernel deadlocks while mounting the image

[Bug 215712] New: kernel deadlocks while mounting the image

[bugzilla-daemon]

https://bugzilla.kernel.org/show_bug.cgi?id=215712

            Bug ID: 215712
           Summary: kernel deadlocks while mounting the image
           Product: File System
           Version: 2.5
    Kernel Version: 5.15.4
          Hardware: All
                OS: Linux
              Tree: Mainline
            Status: NEW
          Severity: normal
          Priority: P1
         Component: ext4
          Assignee: fs_ext4@kernel-bugs.osdl.org
          Reporter: yanming@tju.edu.cn
        Regression: No

I have created an image with mkfs.ext4, and modified some of the metadata of
the image. Unfortunately, when I tried to mount the image with a loop device,
the kernel deadlocked. I have attempted many ways to stop the mount process,
even executed a 'kill' command, but they are failed, only what I can do is to
reboot the system. Can anyone tell me why the kernel deadlocked, and how can I
fix this problem?

I have upload the image to the Google Drive
(https://drive.google.com/file/d/1NjUKdMufpoiyMscpFMdbiwOzyOios-aa/view?usp=sharing).
Looking forward to getting a reply :)

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[Bug 215712] kernel deadlocks while mounting the image

[bugzilla-daemon]

https://bugzilla.kernel.org/show_bug.cgi?id=215712

--- Comment #1 from Artem S. Tashkinov (aros@gmx.com) ---
(In reply to bughunter from comment #0)
> I have created an image with mkfs.ext4, and modified some of the metadata of
> the image. Unfortunately, when I tried to mount the image with a loop
> device, the kernel deadlocked. I have attempted many ways to stop the mount
> process, even executed a 'kill' command, but they are failed, only what I
> can do is to reboot the system. Can anyone tell me why the kernel
> deadlocked, and how can I fix this problem?

That's a bug in the kernel, this situation shouldn't happen. Hopefully someone
will debug and fix this.

In the meanwhile it would be great if you confirmed that 5.17 is also affected.

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[Bug 215712] kernel deadlocks while mounting the image

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https://bugzilla.kernel.org/show_bug.cgi?id=215712

--- Comment #2 from bughunter (yanming@tju.edu.cn) ---
Thank you for prompt reply! I have tested this bug on kernel v5.17, and the
problem still exists.

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[Bug 215712] kernel deadlocks while mounting the image

[bugzilla-daemon]

https://bugzilla.kernel.org/show_bug.cgi?id=215712

Christian Kujau (lists@nerdbynature.de) changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |lists@nerdbynature.de

--- Comment #3 from Christian Kujau (lists@nerdbynature.de) ---
A 5.17 kernel *is* able to mount the image here, but it takes quite some time
to complete:

=======================================
$ time mount -v -t ext4 -o loop,ro,debug tmp.img /mnt/disk/
mount: /dev/loop0 mounted on /mnt/disk.

real    1m32.694s
user    0m0.008s
sys     1m32.665s
=======================================

During that time the CPU is spinning like crazy, but I don't know how to debug
this further as to why it's spinning. perf comes to mind, but maybe something
more ext4 specific is more useful here. dmesg shows, for this mount operation:

=======================================
[  188.269405] [EXT4 FS bs=1024, gc=2, bpg=8192, ipg=2048, mo=a802c818,
mo2=0002]
[  280.932637] EXT4-fs (loop0): mounted filesystem with ordered data mode.
Quota mode: disabled.
[  595.249319] EXT4-fs (loop0): error count since last fsck: 1
[  595.250559] EXT4-fs (loop0): initial error at time 1647888893:
ext4_mb_generate_buddy:756
[  595.253403] EXT4-fs (loop0): last error at time 1647888893:
ext4_mb_generate_buddy:756
=======================================

@Ming, can you share details on how the image has been modified?

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[Bug 215712] kernel deadlocks while mounting the image

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https://bugzilla.kernel.org/show_bug.cgi?id=215712

--- Comment #4 from bughunter (yanming@tju.edu.cn) ---
I modified an original image by replacing the value of its metadata and
recalculating the checksum value, unfortunately I did not record the
modification process. The corresponding source image before modification is
provided at
(https://drive.google.com/file/d/10Pf8E4OwHH7UDVhP3-mxhQuyijvHO3lE/view?usp=sharing).
Hope you have a way to compare the difference between these two images.

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[Bug 215712] kernel deadlocks while mounting the image

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https://bugzilla.kernel.org/show_bug.cgi?id=215712

--- Comment #5 from Christian Kujau (lists@nerdbynature.de) ---
Another attempt to mount the image through trace-cmd took an hour to complete
and produced a trace.dat file, good thing btrfs compression shrank that down to
18 GB :-)

$ trace-cmd record -e ext4 mount -v -t ext4 -o loop,ro,debug ~/tmp.img
/mnt/test/
$ trace-cmd hist
  %-2110.90  (599) mount    ext4_es_lookup_extent_enter #2097643693
         |
         --- *ext4_es_lookup_extent_enter*

  %-2110.90  (599) mount     ext4_es_lookup_extent_exit #2097643669
         |
         --- *ext4_es_lookup_extent_exit*

  %-0.29  (33) kswapd0           ext4_es_shrink_count #292356
         |
         --- *ext4_es_shrink_count*

  %-0.00  (597) trace-cmd           ext4_es_shrink_count #2592
         |
         --- *ext4_es_shrink_count*
[....]

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[Bug 215712] kernel deadlocks while mounting the image

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https://bugzilla.kernel.org/show_bug.cgi?id=215712

--- Comment #6 from bughunter (yanming@tju.edu.cn) ---
Why does the 'mount' command take so long when using such a small image?

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