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Long Li 82c59a86a2 iomap: fix zero padding data issue in concurrent append writes 
[ Upstream commit 51d20d1dac ]

During concurrent append writes to XFS filesystem, zero padding data
may appear in the file after power failure. This happens due to imprecise
disk size updates when handling write completion.

Consider this scenario with concurrent append writes same file:

  Thread 1:                  Thread 2:
  ------------               -----------
  write [A, A+B]
  update inode size to A+B
  submit I/O [A, A+BS]
                             write [A+B, A+B+C]
                             update inode size to A+B+C
  <I/O completes, updates disk size to min(A+B+C, A+BS)>
  <power failure>

After reboot:
  1) with A+B+C < A+BS, the file has zero padding in range [A+B, A+B+C]

  |<         Block Size (BS)      >|
  |DDDDDDDDDDDDDDDD0000000000000000|
  ^               ^        ^
  A              A+B     A+B+C
                         (EOF)

  2) with A+B+C > A+BS, the file has zero padding in range [A+B, A+BS]

  |<         Block Size (BS)      >|<           Block Size (BS)    >|
  |DDDDDDDDDDDDDDDD0000000000000000|00000000000000000000000000000000|
  ^               ^                ^               ^
  A              A+B              A+BS           A+B+C
                                  (EOF)

  D = Valid Data
  0 = Zero Padding

The issue stems from disk size being set to min(io_offset + io_size,
inode->i_size) at I/O completion. Since io_offset+io_size is block
size granularity, it may exceed the actual valid file data size. In
the case of concurrent append writes, inode->i_size may be larger
than the actual range of valid file data written to disk, leading to
inaccurate disk size updates.

This patch modifies the meaning of io_size to represent the size of
valid data within EOF in an ioend. If the ioend spans beyond i_size,
io_size will be trimmed to provide the file with more accurate size
information. This is particularly useful for on-disk size updates
at completion time.

After this change, ioends that span i_size will not grow or merge with
other ioends in concurrent scenarios. However, these cases that need
growth/merging rarely occur and it seems no noticeable performance impact.
Although rounding up io_size could enable ioend growth/merging in these
scenarios, we decided to keep the code simple after discussion [1].

Another benefit is that it makes the xfs_ioend_is_append() check more
accurate, which can reduce unnecessary end bio callbacks of xfs_end_bio()
in certain scenarios, such as repeated writes at the file tail without
extending the file size.

Link [1]: https://patchwork.kernel.org/project/xfs/patch/20241113091907.56937-1-leo.lilong@huawei.com

Fixes: ae259a9c85 ("fs: introduce iomap infrastructure") # goes further back than this
Signed-off-by: Long Li <leo.lilong@huawei.com>
Link: https://lore.kernel.org/r/20241209114241.3725722-3-leo.lilong@huawei.com
Reviewed-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
History 2025-01-17 13:40:34 +01:00
arch ARC: build: Try to guess GCC variant of cross compiler 2025-01-09 13:33:47 +01:00
block block: lift bio_is_zone_append to bio.h 2025-01-09 13:33:32 +01:00
certs sign-file,extract-cert: use pkcs11 provider for OPENSSL MAJOR >= 3 2024-09-20 19:52:48 +03:00
crypto crypto: ecdsa - Avoid signed integer overflow on signature decoding 2024-12-14 20:03:36 +01:00
Documentation fs/writeback: convert wbc_account_cgroup_owner to take a folio 2025-01-17 13:40:33 +01:00
drivers gve: trigger RX NAPI instead of TX NAPI in gve_xsk_wakeup 2025-01-09 13:33:54 +01:00
fs iomap: fix zero padding data issue in concurrent append writes 2025-01-17 13:40:34 +01:00
include iomap: fix zero padding data issue in concurrent append writes 2025-01-17 13:40:34 +01:00
init Compiler Attributes: disable __counted_by for clang < 19.1.3 2024-12-05 14:02:45 +01:00
io_uring io_uring/rw: fix downgraded mshot read 2025-01-09 13:33:51 +01:00
ipc ipc: fix memleak if msg_init_ns failed in create_ipc_ns 2024-12-05 14:03:02 +01:00
kernel fgraph: Add READ_ONCE() when accessing fgraph_array[] 2025-01-09 13:33:52 +01:00
lib maple_tree: reload mas before the second call for mas_empty_area 2025-01-09 13:33:50 +01:00
LICENSES LICENSES: add 0BSD license text 2024-09-01 20:43:24 -07:00
mm mm: hugetlb: independent PMD page table shared count 2025-01-09 13:33:54 +01:00
net mptcp: don't always assume copied data in mptcp_cleanup_rbuf() 2025-01-09 13:33:55 +01:00
rust rust: kbuild: set bindgen's Rust target version 2024-12-19 18:13:22 +01:00
samples samples/bpf: Fix a resource leak 2024-12-14 20:03:46 +01:00
scripts scripts/sorttable: fix orc_sort_cmp() to maintain symmetry and transitivity 2025-01-09 13:33:50 +01:00
security selinux: ignore unknown extended permissions 2025-01-09 13:33:32 +01:00
sound ALSA: seq: oss: Fix races at processing SysEx messages 2025-01-09 13:33:49 +01:00
tools bpf: consider that tail calls invalidate packet pointers 2025-01-09 13:33:47 +01:00
usr initramfs: shorten cmd_initfs in usr/Makefile 2024-07-16 01:07:52 +09:00
virt KVM: x86: switch hugepage recovery thread to vhost_task 2024-12-05 14:02:43 +01:00
.clang-format clang-format: Update with v6.11-rc1's for_each macro list 2024-08-02 13:20:31 +02:00
.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 Kbuild updates for v6.12 2024-09-24 13:02:06 -07:00
.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 location of media main tree 2024-12-05 14:02:42 +01:00
Makefile Linux 6.12.9 2025-01-09 13:33:55 +01:00
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.