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Qu Wenruo 39a93e1c9d btrfs: do not allow relocation of partially dropped subvolumes 
commit 4289b494ac upstream.

[BUG]
There is an internal report that balance triggered transaction abort,
with the following call trace:

  item 85 key (594509824 169 0) itemoff 12599 itemsize 33
          extent refs 1 gen 197740 flags 2
          ref#0: tree block backref root 7
  item 86 key (594558976 169 0) itemoff 12566 itemsize 33
          extent refs 1 gen 197522 flags 2
          ref#0: tree block backref root 7
 ...
 BTRFS error (device loop0): extent item not found for insert, bytenr 594526208 num_bytes 16384 parent 449921024 root_objectid 934 owner 1 offset 0
 BTRFS error (device loop0): failed to run delayed ref for logical 594526208 num_bytes 16384 type 182 action 1 ref_mod 1: -117
 ------------[ cut here ]------------
 BTRFS: Transaction aborted (error -117)
 WARNING: CPU: 1 PID: 6963 at ../fs/btrfs/extent-tree.c:2168 btrfs_run_delayed_refs+0xfa/0x110 [btrfs]

And btrfs check doesn't report anything wrong related to the extent
tree.

[CAUSE]
The cause is a little complex, firstly the extent tree indeed doesn't
have the backref for 594526208.

The extent tree only have the following two backrefs around that bytenr
on-disk:

        item 65 key (594509824 METADATA_ITEM 0) itemoff 13880 itemsize 33
                refs 1 gen 197740 flags TREE_BLOCK
                tree block skinny level 0
                (176 0x7) tree block backref root CSUM_TREE
        item 66 key (594558976 METADATA_ITEM 0) itemoff 13847 itemsize 33
                refs 1 gen 197522 flags TREE_BLOCK
                tree block skinny level 0
                (176 0x7) tree block backref root CSUM_TREE

But the such missing backref item is not an corruption on disk, as the
offending delayed ref belongs to subvolume 934, and that subvolume is
being dropped:

        item 0 key (934 ROOT_ITEM 198229) itemoff 15844 itemsize 439
                generation 198229 root_dirid 256 bytenr 10741039104 byte_limit 0 bytes_used 345571328
                last_snapshot 198229 flags 0x1000000000001(RDONLY) refs 0
                drop_progress key (206324 EXTENT_DATA 2711650304) drop_level 2
                level 2 generation_v2 198229

And that offending tree block 594526208 is inside the dropped range of
that subvolume.  That explains why there is no backref item for that
bytenr and why btrfs check is not reporting anything wrong.

But this also shows another problem, as btrfs will do all the orphan
subvolume cleanup at a read-write mount.

So half-dropped subvolume should not exist after an RW mount, and
balance itself is also exclusive to subvolume cleanup, meaning we
shouldn't hit a subvolume half-dropped during relocation.

The root cause is, there is no orphan item for this subvolume.
In fact there are 5 subvolumes from around 2021 that have the same
problem.

It looks like the original report has some older kernels running, and
caused those zombie subvolumes.

Thankfully upstream commit 8d488a8c7b ("btrfs: fix subvolume/snapshot
deletion not triggered on mount") has long fixed the bug.

[ENHANCEMENT]
For repairing such old fs, btrfs-progs will be enhanced.

Considering how delayed the problem will show up (at run delayed ref
time) and at that time we have to abort transaction already, it is too
late.

Instead here we reject any half-dropped subvolume for reloc tree at the
earliest time, preventing confusion and extra time wasted on debugging
similar bugs.

CC: stable@vger.kernel.org # 5.15+
Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
History 2025-08-20 18:30:54 +02:00
arch MIPS: lantiq: falcon: sysctrl: fix request memory check logic 2025-08-20 18:30:43 +02:00
block block: Introduce bio_needs_zone_write_plugging() 2025-08-20 18:30:51 +02:00
certs sign-file,extract-cert: use pkcs11 provider for OPENSSL MAJOR >= 3 2024-09-20 19:52:48 +03:00
crypto crypto: jitter - fix intermediary handling 2025-08-20 18:30:42 +02:00
Documentation Documentation: ACPI: Fix parent device references 2025-08-20 18:30:15 +02:00
drivers cdc-acm: fix race between initial clearing halt and open 2025-08-20 18:30:52 +02:00
fs btrfs: do not allow relocation of partially dropped subvolumes 2025-08-20 18:30:54 +02:00
include block: Introduce bio_needs_zone_write_plugging() 2025-08-20 18:30:51 +02:00
init io_uring: fix breakage in EXPERT menu 2025-08-15 12:13:32 +02:00
io_uring io_uring/poll: fix POLLERR handling 2025-07-24 08:56:23 +02:00
ipc ipc: fix to protect IPCS lookups using RCU 2025-06-27 11:11:22 +01:00
kernel printk: nbcon: Allow reacquire during panic 2025-08-20 18:30:47 +02:00
lib lib/sbitmap: convert shallow_depth from one word to the whole sbitmap 2025-08-20 18:30:49 +02:00
LICENSES LICENSES: add 0BSD license text 2024-09-01 20:43:24 -07:00
mm mm/damon/core: commit damos->target_nid 2025-08-20 18:30:51 +02:00
net vsock/virtio: Resize receive buffers so that each SKB fits in a 4K page 2025-08-20 18:30:40 +02:00
rust rust: use #[used(compiler)] to fix build and modpost with Rust >= 1.89.0 2025-07-24 08:56:37 +02:00
samples samples: mei: Fix building on musl libc 2025-08-15 12:13:38 +02:00
scripts kconfig: lxdialog: fix 'space' to (de)select options 2025-08-20 18:30:48 +02:00
security apparmor: fix x_table_lookup when stacking is not the first entry 2025-08-20 18:30:47 +02:00
sound ASoC: fsl_sai: replace regmap_write with regmap_update_bits 2025-08-20 18:30:50 +02:00
tools tools/power turbostat: Handle cap_get_proc() ENOSYS 2025-08-20 18:30:49 +02:00
usr kbuild: hdrcheck: fix cross build with clang 2025-03-13 13:02:18 +01:00
virt KVM: Allow CPU to reschedule while setting per-page memory attributes 2025-07-17 18:37:08 +02:00
.clang-format clang-format: Update with v6.11-rc1's for_each macro list 2024-08-02 13:20:31 +02:00
.clippy.toml rust: give Clippy the minimum supported Rust version 2025-08-01 09:48:44 +01:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.editorconfig .editorconfig: remove trim_trailing_whitespace option 2024-06-13 16:47:52 +02:00
.get_maintainer.ignore Add Jeff Kirsher to .get_maintainer.ignore 2024-03-08 11:36:54 +00:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore rust: introduce .clippy.toml 2025-03-13 13:01:42 +01:00
.mailmap mailmap: add entry for Thorsten Blum 2024-11-07 14:14:59 -08:00
.rustfmt.toml rust: add .rustfmt.toml 2022-09-28 09:02:20 +02:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: Remove self from DSA entry 2024-11-03 12:52:38 -08:00
Kbuild Kbuild updates for v6.1 2022-10-10 12:00:45 -07:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS MAINTAINERS: Update Alexey Makhalov's email address 2025-05-22 14:29:46 +02:00
Makefile Linux 6.12.42 2025-08-15 12:14:14 +02:00
README README: Fix spelling 2024-03-18 03:36:32 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.