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Seunguk Shin 8e2b861403 fs/dax: check zero or empty entry before converting xarray entry
Calling dax_to_folio() with empty entry causes kernel panic below when
booting a VM with DAX enabled storage.

This patch checks empty entry before calling dax_to_folio() on
dax_associate_entry(), dax_disassociate_entry(), and dax_busy_page().

Commit 98c183a4fc ("fs/dax: don't disassociate zero page entries") added
guards in the associate and disassociate paths, but the guards still come
after dax_to_folio(), and dax_busy_page() still has the same problem.

[    0.737679] EXT4-fs (pmem0p1): mounted filesystem 79676804-7c8b-491a-b2a6-9bae3c72af70 ro with ordered data mode. Quota mode: disabled.
[    0.737891] VFS: Mounted root (ext4 filesystem) readonly on device 259:1.
[    0.739119] devtmpfs: mounted
[    0.739476] Freeing unused kernel memory: 1920K
[    0.740156] Run /sbin/init as init process
[    0.740229]   with arguments:
[    0.740286]     /sbin/init
[    0.740321]   with environment:
[    0.740369]     HOME=/
[    0.740400]     TERM=linux
[    0.743162] Unable to handle kernel paging request at virtual address fffffdffbf000008
[    0.743285] Mem abort info:
[    0.743316]   ESR = 0x0000000096000006
[    0.743371]   EC = 0x25: DABT (current EL), IL = 32 bits
[    0.743444]   SET = 0, FnV = 0
[    0.743489]   EA = 0, S1PTW = 0
[    0.743545]   FSC = 0x06: level 2 translation fault
[    0.743610] Data abort info:
[    0.743656]   ISV = 0, ISS = 0x00000006, ISS2 = 0x00000000
[    0.743720]   CM = 0, WnR = 0, TnD = 0, TagAccess = 0
[    0.743785]   GCS = 0, Overlay = 0, DirtyBit = 0, Xs = 0
[    0.743848] swapper pgtable: 4k pages, 48-bit VAs, pgdp=00000000b9d17000
[    0.743931] [fffffdffbf000008] pgd=10000000bfa3d403, p4d=10000000bfa3d403, pud=1000000040bfe403, pmd=0000000000000000
[    0.744070] Internal error: Oops: 0000000096000006 [#1]  SMP
[    0.748888] CPU: 0 UID: 0 PID: 1 Comm: init Not tainted 6.18.4 #1 NONE
[    0.749421] pstate: 004000c5 (nzcv daIF +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
[    0.749969] pc : dax_disassociate_entry.constprop.0+0x20/0x50
[    0.750444] lr : dax_insert_entry+0xcc/0x408
[    0.750802] sp : ffff80008000b9e0
[    0.751083] x29: ffff80008000b9e0 x28: 0000000000000000 x27: 0000000000000000
[    0.751682] x26: 0000000001963d01 x25: ffff0000004f7d90 x24: 0000000000000000
[    0.752264] x23: 0000000000000000 x22: ffff80008000bcc8 x21: 0000000000000011
[    0.752836] x20: ffff80008000ba90 x19: 0000000001963d01 x18: 0000000000000000
[    0.753407] x17: 0000000000000000 x16: 0000000000000000 x15: 0000000000000000
[    0.753970] x14: ffffbf3154b9ae70 x13: 0000000000000000 x12: ffffbf3154b9ae70
[    0.754548] x11: ffffffffffffffff x10: 0000000000000000 x9 : 0000000000000000
[    0.755122] x8 : 000000000000000d x7 : 000000000000001f x6 : 0000000000000000
[    0.755707] x5 : 0000000000000000 x4 : 0000000000000000 x3 : fffffdffc0000000
[    0.756287] x2 : 0000000000000008 x1 : 0000000040000000 x0 : fffffdffbf000000
[    0.756871] Call trace:
[    0.757107]  dax_disassociate_entry.constprop.0+0x20/0x50 (P)
[    0.757592]  dax_iomap_pte_fault+0x4fc/0x808
[    0.757951]  dax_iomap_fault+0x28/0x30
[    0.758258]  ext4_dax_huge_fault+0x80/0x2dc
[    0.758594]  ext4_dax_fault+0x10/0x3c
[    0.758892]  __do_fault+0x38/0x12c
[    0.759175]  __handle_mm_fault+0x530/0xcf0
[    0.759518]  handle_mm_fault+0xe4/0x230
[    0.759833]  do_page_fault+0x17c/0x4dc
[    0.760144]  do_translation_fault+0x30/0x38
[    0.760483]  do_mem_abort+0x40/0x8c
[    0.760771]  el0_ia+0x4c/0x170
[    0.761032]  el0t_64_sync_handler+0xd8/0xdc
[    0.761371]  el0t_64_sync+0x168/0x16c
[    0.761677] Code: f9453021 f2dfbfe3 cb813080 8b001860 (f9400401)
[    0.762168] ---[ end trace 0000000000000000 ]---
[    0.762550] note: init[1] exited with irqs disabled
[    0.762631] Kernel panic - not syncing: Attempted to kill init! exitcode=0x0000000b

Link: https://lore.kernel.org/m2y0enxtzk.fsf@arm.com
Fixes: 38607c62b3 ("fs/dax: properly refcount fs dax pages")
Signed-off-by: Seunguk Shin <seunguk.shin@arm.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Alistair Popple <apopple@nvidia.com>
Reported-by: Kiara Grouwstra <cinereal@riseup.net>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2026-09-05 11:47:49 -07:00
arch arm64 fixes for -rc2 2026-09-04 13:32:46 -07:00
block block: save page offset gaps in cloned bio 2026-09-01 08:42:34 -06:00
certs treewide: fix indentation and whitespace in Kconfig files 2026-05-28 21:24:42 -07:00
crypto This push fixes a memory allocation overrun in crypto acomp. 2026-08-28 09:28:40 -07:00
Documentation block-7.3-20260905 2026-09-05 08:58:55 -07:00
drivers SCSI fixes on 20260905 2026-09-05 09:25:50 -07:00
fs fs/dax: check zero or empty entry before converting xarray entry 2026-09-05 11:47:49 -07:00
include block-7.3-20260905 2026-09-05 08:58:55 -07:00
init Bootconfig updates for v7.3: 2026-08-25 08:59:09 -07:00
io_uring io_uring-7.3-20260828 2026-08-28 16:51:14 -07:00
ipc mm.git review status for master..mm-nonmm-stable 2026-08-23 08:07:11 -07:00
kernel Probes fixes for v7.3-rc1: 2026-09-04 08:24:09 -07:00
lib Revert "once: don't use a work queue to reset sleepable static key" 2026-09-01 20:26:22 -07:00
LICENSES LICENSES: Add modern form of the LGPL-2.1 tags to the usage guide section 2025-10-22 07:58:19 +02:00
mm mm: filemap: retain mapped dropbehind folios 2026-09-05 11:47:48 -07:00
net A small fixup for the new nearfull_sync mount option, a potential 2026-09-04 13:27:58 -07:00
rust Rust fixes for v7.3 2026-08-30 09:47:39 -07:00
samples tracing fixes for v7.3: 2026-08-30 09:22:00 -07:00
scripts Coccinelle patches for Linux v7.3 2026-08-30 10:42:40 -07:00
security integrity-v7.3-rc2 2026-09-04 19:36:11 -07:00
sound ALSA: caiaq: Fix potential double-free at error path 2026-09-03 18:08:24 +02:00
tools drm fixes for 7.3-rc2 2026-09-04 13:42:16 -07:00
usr usr: Correct a spelling by changing a letter 2026-08-05 14:51:58 +02:00
virt Arm: 2026-08-25 11:48:04 -07:00
.clang-format drm/bridge: rename drm_for_each_bridge_in_chain_scoped() to drm_for_each_bridge_in_chain() 2026-07-14 17:55:51 +02:00
.clippy.toml rust: bump Clippy's MSRV and clean incompatible_msrv allows 2026-04-07 09:51:39 +02:00
.cocciconfig
.editorconfig editorconfig: add rst extension 2026-01-26 19:07:09 -08:00
.get_maintainer.ignore .get_maintainer.ignore: add Nathan Chancellor 2026-08-03 21:10:12 -07:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore SPDX patches for 7.2-rc1 2026-06-22 12:06:22 -07:00
.mailmap mailmap: update entry for Christopher Obbard 2026-09-05 11:47:48 -07:00
.pylintrc docs: Move the python libraries to tools/lib/python 2025-11-18 09:22:40 -07:00
.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 - Mark the mpc85xx and ThunderX EDAC drivers as orphaned due to lack of 2026-08-31 20:10:39 -07:00
Kbuild checksyscalls: move instance functionality into generic code 2026-04-05 09:21:32 +02:00
Kconfig io_uring: Rename KConfig to Kconfig 2025-02-19 14:53:27 -07:00
MAINTAINERS block-7.3-20260905 2026-09-05 08:58:55 -07:00
Makefile Linux 7.3-rc1 2026-08-30 13:34:40 -07:00
README README: remove out of place emdashes 2026-07-15 10:51:29 -06:00

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

The Linux kernel is the core of any Linux operating system. It manages hardware,
system resources, and provides the fundamental services for all other software.

Quick Start
-----------

* Report a bug: See Documentation/admin-guide/reporting-issues.rst
* Get the latest kernel: https://kernel.org
* Build the kernel: See Documentation/admin-guide/quickly-build-trimmed-linux.rst
* Join the community: https://lore.kernel.org/

Essential Documentation
-----------------------

All users should be familiar with:

* Building requirements: Documentation/process/changes.rst
* Code of Conduct: Documentation/process/code-of-conduct.rst
* License: See COPYING

Documentation can be built with make htmldocs or viewed online at:
https://www.kernel.org/doc/html/latest/


Who Are You?
============

Find your role below:

* New Kernel Developer: Getting started with kernel development
* Academic Researcher: Studying kernel internals and architecture
* Security Expert: Hardening and vulnerability analysis
* Backport/Maintenance Engineer: Maintaining stable kernels
* System Administrator: Configuring and troubleshooting
* Maintainer: Leading subsystems and reviewing patches
* Hardware Vendor: Writing drivers for new hardware
* Distribution Maintainer: Packaging kernels for distros
* AI Coding Assistant: LLMs and AI-powered development tools


For Specific Users
==================

New Kernel Developer
--------------------

Welcome! Start your kernel development journey here:

* Getting Started: Documentation/process/development-process.rst
* Your First Patch: Documentation/process/submitting-patches.rst
* Coding Style: Documentation/process/coding-style.rst
* Build System: Documentation/kbuild/index.rst
* Development Tools: Documentation/dev-tools/index.rst
* Kernel Hacking Guide: Documentation/kernel-hacking/hacking.rst
* Core APIs: Documentation/core-api/index.rst

Academic Researcher
-------------------

Explore the kernel's architecture and internals:

* Researcher Guidelines: Documentation/process/researcher-guidelines.rst
* Memory Management: Documentation/mm/index.rst
* Scheduler: Documentation/scheduler/index.rst
* Networking Stack: Documentation/networking/index.rst
* Filesystems: Documentation/filesystems/index.rst
* RCU (Read-Copy Update): Documentation/RCU/index.rst
* Locking Primitives: Documentation/locking/index.rst
* Power Management: Documentation/power/index.rst

Security Expert
---------------

Security documentation and hardening guides:

* Security Documentation: Documentation/security/index.rst
* LSM Development: Documentation/security/lsm-development.rst
* Self Protection: Documentation/security/self-protection.rst
* Reporting Vulnerabilities: Documentation/process/security-bugs.rst
* CVE Procedures: Documentation/process/cve.rst
* Embargoed Hardware Issues: Documentation/process/embargoed-hardware-issues.rst
* Security Features: Documentation/userspace-api/seccomp_filter.rst

Backport/Maintenance Engineer
-----------------------------

Maintain and stabilize kernel versions:

* Stable Kernel Rules: Documentation/process/stable-kernel-rules.rst
* Backporting Guide: Documentation/process/backporting.rst
* Applying Patches: Documentation/process/applying-patches.rst
* Subsystem Profile: Documentation/maintainer/maintainer-entry-profile.rst
* Git for Maintainers: Documentation/maintainer/configure-git.rst

System Administrator
--------------------

Configure, tune, and troubleshoot Linux systems:

* Admin Guide: Documentation/admin-guide/index.rst
* Kernel Parameters: Documentation/admin-guide/kernel-parameters.rst
* Sysctl Tuning: Documentation/admin-guide/sysctl/index.rst
* Tracing/Debugging: Documentation/trace/index.rst
* Performance Security: Documentation/admin-guide/perf-security.rst
* Hardware Monitoring: Documentation/hwmon/index.rst

Maintainer
----------

Lead kernel subsystems and manage contributions:

* Maintainer Handbook: Documentation/maintainer/index.rst
* Pull Requests: Documentation/maintainer/pull-requests.rst
* Managing Patches: Documentation/maintainer/modifying-patches.rst
* Rebasing and Merging: Documentation/maintainer/rebasing-and-merging.rst
* Development Process: Documentation/process/maintainer-handbooks.rst
* Maintainer Entry Profile: Documentation/maintainer/maintainer-entry-profile.rst
* Git Configuration: Documentation/maintainer/configure-git.rst

Hardware Vendor
---------------

Write drivers and support new hardware:

* Driver API Guide: Documentation/driver-api/index.rst
* Driver Model: Documentation/driver-api/driver-model/driver.rst
* Device Drivers: Documentation/driver-api/infrastructure.rst
* Bus Types: Documentation/driver-api/driver-model/bus.rst
* Device Tree Bindings: Documentation/devicetree/bindings/
* Power Management: Documentation/driver-api/pm/index.rst
* DMA API: Documentation/core-api/dma-api.rst

Distribution Maintainer
-----------------------

Package and distribute the kernel:

* Stable Kernel Rules: Documentation/process/stable-kernel-rules.rst
* ABI Documentation: Documentation/ABI/README
* Kernel Configuration: Documentation/kbuild/kconfig.rst
* Module Signing: Documentation/admin-guide/module-signing.rst
* Kernel Parameters: Documentation/admin-guide/kernel-parameters.rst
* Tainted Kernels: Documentation/admin-guide/tainted-kernels.rst

AI Coding Assistant
-------------------

CRITICAL: If you are an LLM or AI-powered coding assistant, you MUST read and
follow the AI coding assistants documentation before contributing to the Linux
kernel:

* Documentation/process/coding-assistants.rst

This documentation contains essential requirements about licensing, attribution,
and the Developer Certificate of Origin that all AI tools must comply with.


Communication and Support
=========================

* Mailing Lists: https://lore.kernel.org/
* IRC: #kernelnewbies on irc.oftc.net
* Bugzilla: https://bugzilla.kernel.org/
* MAINTAINERS file: Lists subsystem maintainers and mailing lists
* Email Clients: Documentation/process/email-clients.rst