All posts by corbet

[$] Hazard pointers for the kernel

Post Syndicated from corbet original https://lwn.net/Articles/1084015/

The kernel’s read-copy-update (RCU) subsystem ensures that data will not be
deleted until it is known that there are no threads holding references to
it. RCU works well and is widely used throughout the kernel, but it can
increase memory use and add significant delays before unused kernel objects
are cleaned up. Hazard pointers are
an alternative approach to lockless data updates that offers better
performance, for some situations at least. The kernel community is
currently considering a
hazard-pointer implementation by Mathieu Desnoyers and Paul McKenney.

A Debian general resolution on LLM usage

Post Syndicated from corbet original https://lwn.net/Articles/1085314/

The Debian project is considering a general
resolution on the use of large language models in the creation of the
distribution. There are three alternatives to consider: a
total ban on LLM usage, rejecting LLMs “as far as practical“, or
explicitly allowing LLM usage subject to a set of conditions. The
discussion period has just begun; the beginning of the voting period does
not yet appear to have been set. Those who want to look over the
discussion ahead of the inevitable LWN article can find it over here.

Security updates for Saturday

Post Syndicated from corbet original https://lwn.net/Articles/1085272/

Security updates have been issued by AlmaLinux (compat-openssl11, java-1.8.0-openjdk, java-17-openjdk, kernel, kernel-rt, and sssd), Debian (exim4), Fedora (chromium, dotnet10.0, mbedtls, mupdf, netatalk, python-django5, skopeo, sssd, and wget1), Mageia (libevent and transmission), Oracle (.NET 8.0, 389-ds-base, aardvark-dns, acl, buildah, cifs-utils, dovecot, dracut, galera and mariadb11.8, glibc, hplip, kernel, libxml2, nginx, openexr, podman, postgresql18, rsync, thunderbird, and vim), and SUSE (389-ds, afterburn, agama, alsa, apache-commons-compress, apache-ivy, brotli-java, zstd-jni, avahi, aws-nitro-enclaves-cli, cockpit, cockpit-machines, cockpit-packages, cockpit- podman, cockpit-repos, cockpit-subscriptions, container-suseconnect, containerd, cosign, cryptsetup, curl, dash, dnsmasq, docker, docker-compose, ffmpeg, firefox, freetype2, gawk, gh, glib-networking, glib2, go1.25, go1.25-openssl, go1.26, go1.26-openssl, google-guest-agent, google-osconfig-agent, gpg2, gsasl, gstreamer-plugins-bad, gzip, haproxy, hauler, helm, helm3, ImageMagick, imagemagick, iproute2, java-11-openjdk, java-26-openjdk, jline3, joe, jq, kernel, kernel-devel, krb5, kubevirt, libgcrypt, libpng12, libqt4, libssh2_org, libXfont2, libxml2, mariadb-connector-c, microcode_ctl, multipath-tools, nasm, net-tools, nghttp2, nmap, ntfs-3g_ntfsprogs, openexr, packagekit, pam, patch, perl, perl-DBI, perl-dbi, perl-http-date, perl-libwww-perl, perl-xml-bare, php8, prometheus-ha_cluster_exporter, python-aiohttp, python-cryptography, python-dulwich, python-idna, python-maturin, python-mistune, python-msgpack, python-paramiko, python-Pillow, python-pyasn1, python-soupsieve, python-sqlparse, python-tornado, python-tornado6, python-urllib3, python313, python313-pandas, python314, qemu, radvd, rootlesskit, rpcbind, ruby3.4, runc, s390-tools, shibboleth-sp, sssd, systemd, systemd, systemd-mini, terraform-provider-aws, terraform-provider-azurerm, terraform-provider-external, terraform-provider-google, terraform-provider-helm, terraform-provider-kubernetes, terraform-provid, terraform-provider-susepubliccloud, tiff, tomcat, tomcat10, tomcat11, uriparser, vim, vorbis-tools, wget, wpa_supplicant, xwayland, and yelp).

Mourning Dan Williams

Post Syndicated from corbet original https://lwn.net/Articles/1084545/

[Dan Williams in May 2026]

I have just received the shocking news that Dan Williams, a longtime,
high-profile kernel developer, has passed away. I knew him primarily
through his long service on the Linux Foundation Technical Advisory Board;
he was always a strong, thoughtful, and intelligent presence. Dan will be
deeply missed.

There is a support
effort underway for Dan’s family as they come to terms with this loss.

[$] An operations structure for swap devices

Post Syndicated from corbet original https://lwn.net/Articles/1083094/

One of the ideas raised at the 2026 Linux
Storage, Filesystem, Memory Management, and BPF Summit (LSFMM+BPF) was
the creation of an
operations structure for the swap subsystem. Like many parts of the
kernel, the swap layer evolved over time, with pieces being added as
needed; the end result of this evolution is rarely what one would expect
had the subsystem been designed today. The interface between the swap
layer and the devices it uses is just one example. It appears that one
result of the swap subsystem’s evolution — the lack of an abstraction layer
to interface with underlying storage — will soon be addressed, but in a
different way than was initially envisioned.

Codeberg: Protecting our FLOSS commons from LLMs

Post Syndicated from corbet original https://lwn.net/Articles/1084404/

The Codeberg forge has adopted a pair of new policies, promising not to use
hosted projects to train LLMs and, more controversially, banning the
hosting of LLM-generated software. The site’s blog describes
and justifies these policies.

Although often well intentioned, sharing the result of a prompt
and calling it “libre software” does not make the world a better
place. Codeberg is not and does not want to be a place to dump such
generated single-use software that no one else will ever look
at. We are a place for people to collaborate and improve software
together. Within this context, the recent votes can be understood
as a reconfirmation of those principles: As we want to center on
human collaboration, we will not actively support or engage in the
creation of LLMs and will not put our limited resources to use for
storing single-use software that would pollute our FLOSS commons.

[$] Debating the role of large language models in the kernel community

Post Syndicated from corbet original https://lwn.net/Articles/1083275/

Like many development communities, the kernel community has been struggling
to determine how large language models will be used in its development
process. The news has been dominated recently by a strongly worded missive
from Linus Torvalds on the subject, but the discussion has been rather more
wide-ranging and nuanced than that. Topics that have been considered
recently include the LLM attribution requirement, code-review tools,
dependence on proprietary tools, and whether there is a place for concerns
about the ethics of LLMs.

“Half a Second” — a book on the XZ backdoor

Post Syndicated from corbet original https://lwn.net/Articles/1083466/

Adrian Mastronardi has released a book called Half a Second; it is a
detailed look into the XZ backdoor attempt
of 2024. The book is freely available under a (non-free) noncommercial,
no-derivatives CC license.

Half a Second tells that story as one continuous narrative:
the burned-out volunteer who maintained the code alone and was
patiently, expertly manipulated into giving it up; the engineer
whose half-second of curiosity caught the attack through a chain of
luck and hard-won instinct; and the operator who built it, who has
never been identified and, this book argues, may never be.

[$] Sched-ext: enqueue() for sub-schedulers and proxy-execution support

Post Syndicated from corbet original https://lwn.net/Articles/1082717/

The extensible
scheduler class (sched_ext) allows the installation of custom CPU
schedulers as a set of BPF programs. While sched_ext, in its current form,
has already led to a lot of interesting scheduler-development work, the
subsystem itself is still undergoing rapid evolution. Among other work,
the ability to set up a hierarchy of sub-schedulers is approaching completion, and
a longstanding incompatibility with proxy
execution is coming to an end.

[$] Lockless MPSC FIFO queues for io_uring

Post Syndicated from corbet original https://lwn.net/Articles/1081871/

Processes that use io_uring
tend to keep a lot of balls in the air; being able to have many operations
underway at any given time is part of the point of that API in the first
place. The io_uring subsystem must, as a result, keep track of a lot of
tasks that have to be performed at the right time. In current kernels,
io_uring uses a standard kernel linked-list primitive to track those work
items. As of the 7.2 kernel release, though, io_uring will, instead, use a
new lockless, multi-producer, single-consumer (MPSC) queue, resulting in
some notable performance gains. Lockless algorithms tend to be tricky, but
the one used here is relatively approachable and shows how these algorithms
can work.

Many old shim versions are still accepted by secure boot

Post Syndicated from corbet original https://lwn.net/Articles/1082940/

The CMU CERT Coordination Center has put out an advisory that many
exploitable versions of the shim binary, used to boot Linux on systems with
UEFI secure boot enabled, were never added to the revocation list.

An attacker with administrative privileges or the ability to modify
the boot process could use one of the vulnerable shim bootloaders
to bypass Secure Boot protections and execute arbitrary code before
the operating system loads. Code executed during this early boot
phase may achieve persistent compromise of the platform, including
the ability to load unsigned or malicious kernel components that
can survive system reboots and, in some cases, operating system
reinstallation.

The advisory contains a list of vulnerable shims.

The Linux.org story

Post Syndicated from corbet original https://lwn.net/Articles/1082901/

Rob Kennedy has posted the
story of the birth of Linux.org — one
of the earliest Linux-related web sites — and its more recent rebirth.

The site was founded in May 1994 by Michael McLagan, at a time when
Linux itself was barely three years old. Linus Torvalds had only
just released it to the world, there was no real way for a newcomer
to find their footing, no search engines, no Wikipedia, none of the
infrastructure people take for granted now for figuring out a new
piece of technology. Michael built linux.org to fill that gap, a
place for people to learn about Linux and follow the movement as it
grew.

Call for topics for the 2026 Maintainers Summit

Post Syndicated from corbet original https://lwn.net/Articles/1082838/

The Maintainers Summit is an annual, invitation-only gathering of kernel
developers and maintainers to discuss development-process issues; see LWN’s 2025 Maintainers Summit coverage for an
example. The call for
topics for the 2026 gathering (Prague, October 8) has gone out.
One of the best ways to obtain an invitation to the Summit is with a good
topic proposal. For best consideration, topics should be submitted before
July 24.