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huang-jl a4315e409a io_uring: fix nr_segs calculation in io_import_kbuf 
[ Upstream commit 114ea9bbaf ]

io_import_kbuf() calculates nr_segs incorrectly when iov_offset is
non-zero after iov_iter_advance(). It doesn't account for the partial
consumption of the first bvec.

The problem comes when meet the following conditions:
1. Use UBLK_F_AUTO_BUF_REG feature of ublk.
2. The kernel will help to register the buffer, into the io uring.
3. Later, the ublk server try to send IO request using the registered
   buffer in the io uring, to read/write to fuse-based filesystem, with
O_DIRECT.

>From a userspace perspective, the ublk server thread is blocked in the
kernel, and will see "soft lockup" in the kernel dmesg.

When ublk registers a buffer with mixed-size bvecs like [4K]*6 + [12K]
and a request partially consumes a bvec, the next request's nr_segs
calculation uses bvec->bv_len instead of (bv_len - iov_offset).

This causes fuse_get_user_pages() to loop forever because nr_segs
indicates fewer pages than actually needed.

Specifically, the infinite loop happens at:
fuse_get_user_pages()
  -> iov_iter_extract_pages()
    -> iov_iter_extract_bvec_pages()
Since the nr_segs is miscalculated, the iov_iter_extract_bvec_pages
returns when finding that i->nr_segs is zero. Then
iov_iter_extract_pages returns zero. However, fuse_get_user_pages does
still not get enough data/pages, causing infinite loop.

Example:
  - Bvecs: [4K, 4K, 4K, 4K, 4K, 4K, 12K, ...]
  - Request 1: 32K at offset 0, uses 6*4K + 8K of the 12K bvec
  - Request 2: 32K at offset 32K
    - iov_offset = 8K (8K already consumed from 12K bvec)
    - Bug: calculates using 12K, not (12K - 8K) = 4K
    - Result: nr_segs too small, infinite loop in fuse_get_user_pages.

Fix by accounting for iov_offset when calculating the first segment's
available length.

Fixes: b419bed4f0 ("io_uring/rsrc: ensure segments counts are correct on kbuf buffers")
Signed-off-by: huang-jl <huang-jl@deepseek.com>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
History 2026-01-02 12:56:53 +01:00
arch x86/xen: Fix sparse warning in enlighten_pv.c 2026-01-02 12:56:53 +01:00
block block: fix race between wbt_enable_default and IO submission 2026-01-02 12:56:51 +01:00
certs sign-file,extract-cert: use pkcs11 provider for OPENSSL MAJOR >= 3 2024-09-20 19:52:48 +03:00
crypto crypto: ahash - Zero positive err value in ahash_update_finish 2025-12-18 14:03:12 +01:00
Documentation docs: hwmon: fix link to g762 devicetree binding 2025-12-18 14:03:38 +01:00
drivers spi: cadence-quadspi: Fix clock disable on probe failure path 2026-01-02 12:56:53 +01:00
fs gfs2: Fix use of bio_chain 2026-01-02 12:56:43 +01:00
include inet: frags: flush pending skbs in fqdir_pre_exit() 2026-01-02 12:56:46 +01:00
init printk changes for 6.18 2025-10-04 11:13:11 -07:00
io_uring io_uring: fix nr_segs calculation in io_import_kbuf 2026-01-02 12:56:53 +01:00
ipc namespace-6.18-rc1 2025-09-29 11:20:29 -07:00
kernel livepatch: Match old_sympos 0 and 1 in klp_find_func() 2026-01-02 12:56:39 +01:00
lib lib/vsprintf: Check pointer before dereferencing in time_and_date() 2025-12-18 14:02:58 +01:00
LICENSES LICENSES: Replace the obsolete address of the FSF in the GFDL-1.2 2025-07-24 11:15:39 +02:00
mm shmem: fix recovery on rename failures 2026-01-02 12:56:37 +01:00
net net/handshake: duplicate handshake cancellations leak socket 2026-01-02 12:56:49 +01:00
rust rust: Add -fno-isolate-erroneous-paths-dereference to bindgen_skip_c_flags 2025-11-10 08:37:06 +08:00
samples samples: work around glibc redefining some of our defines wrong 2025-11-21 09:29:02 -08:00
scripts kbuild: Use objtree for module signing key path 2026-01-02 12:56:40 +01:00
security landlock: Fix handling of disconnected directories 2025-12-18 14:03:27 +01:00
sound ALSA: wavefront: Fix integer overflow in sample size validation 2025-12-18 14:03:43 +01:00
tools selftests: ublk: fix overflow in ublk_queue_auto_zc_fallback() 2026-01-02 12:56:50 +01:00
usr gen_init_cpio: Ignore fsync() returning EINVAL on pipes 2025-10-07 09:53:05 -07:00
virt KVM: guest_memfd: Remove bindings on memslot deletion when gmem is dying 2025-11-04 09:16:53 -08:00
.clang-format memblock: drop for_each_free_mem_pfn_range_in_zone_from() 2025-09-14 08:49:03 +03:00
.clippy.toml rust: clean Rust 1.88.0's warning about clippy::disallowed_macros configuration 2025-05-07 00:11:47 +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 MAINTAINERS: remove Alyssa Rosenzweig 2025-09-18 21:17:31 +02:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore .gitignore: ignore compile_commands.json globally 2025-08-12 15:53:55 -07:00
.mailmap 8 hotfixes. 4 are cc:stable, 7 are against mm/. 2025-11-26 12:38:05 -08:00
.pylintrc tools: docs: parse-headers.py: move it from sphinx dir 2025-08-29 15:54:42 -06:00
.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: mark ISDN subsystem as orphan 2025-10-27 17:49:45 -07:00
Kbuild sched: Make migrate_{en,dis}able() inline 2025-09-25 09:57:16 +02:00
Kconfig io_uring: Rename KConfig to Kconfig 2025-02-19 14:53:27 -07:00
MAINTAINERS soc: fixes for 6.18, part 4 2025-11-28 09:57:31 -08:00
Makefile Linux 6.18.2 2025-12-18 14:03:43 +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.