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Yongjian Sun c05033cfc5 ext4: fix e4b bitmap inconsistency reports commit `bdc56a9c46` upstream. A bitmap inconsistency issue was observed during stress tests under mixed huge-page workloads. Ext4 reported multiple e4b bitmap check failures like: ext4_mb_complex_scan_group:2508: group 350, 8179 free clusters as per group info. But got 8192 blocks Analysis and experimentation confirmed that the issue is caused by a race condition between page migration and bitmap modification. Although this timing window is extremely narrow, it is still hit in practice: folio_lock ext4_mb_load_buddy __migrate_folio check ref count folio_mc_copy __filemap_get_folio folio_try_get(folio) ...... mb_mark_used ext4_mb_unload_buddy __folio_migrate_mapping folio_ref_freeze folio_unlock The root cause of this issue is that the fast path of load_buddy only increments the folio's reference count, which is insufficient to prevent concurrent folio migration. We observed that the folio migration process acquires the folio lock. Therefore, we can determine whether to take the fast path in load_buddy by checking the lock status. If the folio is locked, we opt for the slow path (which acquires the lock) to close this concurrency window. Additionally, this change addresses the following issues: When the DOUBLE_CHECK macro is enabled to inspect bitmap-related issues, the following error may be triggered: corruption in group 324 at byte 784(6272): f in copy != ff on disk/prealloc Analysis reveals that this is a false positive. There is a specific race window where the bitmap and the group descriptor become momentarily inconsistent, leading to this error report: ext4_mb_load_buddy ext4_mb_load_buddy __filemap_get_folio(create\|lock) folio_lock ext4_mb_init_cache folio_mark_uptodate __filemap_get_folio(no lock) ...... mb_mark_used mb_mark_used_double mb_cmp_bitmaps mb_set_bits(e4b->bd_bitmap) folio_unlock The original logic assumed that since mb_cmp_bitmaps is called when the bitmap is newly loaded from disk, the folio lock would be sufficient to prevent concurrent access. However, this overlooks a specific race condition: if another process attempts to load buddy and finds the folio is already in an uptodate state, it will immediately begin using it without holding folio lock. Signed-off-by: Yongjian Sun <sunyongjian1@huawei.com> Reviewed-by: Zhang Yi <yi.zhang@huawei.com> Reviewed-by: Baokun Li <libaokun1@huawei.com> Reviewed-by: Jan Kara <jack@suse.cz> Link: https://patch.msgid.link/20260106090820.836242-1-sunyongjian@huaweicloud.com Signed-off-by: Theodore Ts'o <tytso@mit.edu> Cc: stable@kernel.org Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>		History 2026-03-04 07:20:47 -05:00
arch	MIPS: Work around LLVM bug when gp is used as global register variable	2026-03-04 07:20:46 -05:00
block	block: add a bio_add_virt_nofail helper	2026-03-04 07:19:26 -05:00
certs	sign-file,extract-cert: use pkcs11 provider for OPENSSL MAJOR >= 3	2024-09-20 19:52:48 +03:00
crypto	crypto: authencesn - reject too-short AAD (assoclen<8) to match ESP/ESN spec	2026-01-30 10:28:39 +01:00
Documentation	Documentation: tracing: Add PCI tracepoint documentation	2026-03-04 07:19:59 -05:00
drivers	drm/amd/display: Use same max plane scaling limits for all 64 bpp formats	2026-03-04 07:20:46 -05:00
fs	ext4: fix e4b bitmap inconsistency reports	2026-03-04 07:20:47 -05:00
include	net/mlx5: Fix multiport device check over light SFs	2026-03-04 07:20:39 -05:00
init	init: handle bootloader identifier in kernel parameters	2025-10-19 16:33:50 +02:00
io_uring	io_uring/cancel: de-unionize file and user_data in struct io_cancel_data	2026-03-04 07:20:34 -05:00
ipc	ipc: don't audit capability check in ipc_permissions()	2026-03-04 07:20:07 -05:00
kernel	tracing: Remove duplicate ENABLE_EVENT_STR and DISABLE_EVENT_STR macros	2026-03-04 07:20:25 -05:00
lib	objpool: fix the overestimation of object pooling metadata size	2026-03-04 07:20:35 -05:00
LICENSES	LICENSES: add 0BSD license text	2024-09-01 20:43:24 -07:00
mm	mm/hugetlb: fix excessive IPI broadcasts when unsharing PMD tables using mmu_gather	2026-02-19 16:29:55 +01:00
net	icmp: prevent possible overflow in icmp_global_allow()	2026-03-04 07:20:39 -05:00
rust	rust: rbtree: fix documentation typo in CursorMut peek_next method	2026-02-06 16:55:44 +01:00
samples	samples/ftrace: Adjust LoongArch register restore order in direct calls	2026-01-08 10:14:50 +01:00
scripts	scripts: generate_rust_analyzer: Add compiler_builtins -> core dep	2026-02-06 16:55:47 +01:00
security	apparmor: fix aa_label to return state from compount and component match	2026-03-04 07:20:41 -05:00
sound	ASoC: rockchip: i2s-tdm: Use param rate if not provided by set_sysclk	2026-03-04 07:20:46 -05:00
tools	bpftool: Fix truncated netlink dumps	2026-03-04 07:20:38 -05:00
usr	kbuild: uapi: Strip comments before size type check	2025-11-13 15:34:35 -05:00
virt	KVM: Don't clobber irqfd routing type when deassigning irqfd	2026-02-11 13:40:17 +01:00
.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	gpiolib-acpi: Update file references in the Documentation and MAINTAINERS	2026-02-11 13:40:29 +01:00
Makefile	kbuild: Add objtool to top-level clean target	2026-03-04 07:20:35 -05:00
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.