Linux Weekly News

Longtime PyPy developer Antonio Cuni has a lengthy blog post that describes his talk at the recently completed 2025 CPython Core Dev Sprint, held at Arm in Cambridge, UK. The talk, entitled "Tracing JIT and real world Python — aka: what we can learn from PyPy" was meant to try to pass on some of his experiences "optimizing existing code for PyPy at a high-frequency trading firm" to the developers working on the CPython JIT compiler. His goal was to raise awareness of some of the problems he encountered: Until now CPython's performance has been particularly predictable, there are well established "performance tricks" to make code faster, and generally speaking you can mostly reason about the speed of a given piece of code "locally".

Adding a JIT completely changes how we reason about performance of a given program, for two reasons:

1. JITted code can be very fast if your code conforms to the heuristics applied by the JIT compiler, but unexpectedly slow(-ish) otherwise;
2. the speed of a given piece of code might depend heavily on what happens elsewhere in the program, making it much harder to reason about performance locally.

The end result is that modifying a line of code can significantly impact seemingly unrelated code. This effect becomes more pronounced as the JIT becomes more sophisticated.

Cuni also gave a talk on Python performance, which LWN covered, at EuroPython 2025 in July.

The file_operations structure in the kernel is a set of function pointers implementing, as the name would suggest, operations on files. A subsystem that manages objects which can be represented by a file descriptor will provide a file_operations structure providing implementations of the various operations that a user of the file descriptor may want to carry out. The mmap() method, in particular, is invoked when user space calls the mmap() system call to map the object behind a file descriptor into its address space. That method, though, is currently on its way out in a multi-release process that started in 6.17.

The Fedora project has posted a proposal for a policy regarding the use of AI tools when developing for the distribution.

You are responsible for your contributions. AI-generated content must be treated as a suggestion, not as final code or text. It is your responsibility to review, test, and understand everything you submit. Submitting unverified or low-quality machine-generated content (sometimes called "AI slop") creates an unfair review burden on the community and is not an acceptable contribution.

The 6.16.9, 6.12.49, 6.6.108, and 6.1.154 stable kernels have been released. As usual, they all contain important fixes throughout the kernel tree.

Security updates have been issued by AlmaLinux (grub2 and kernel), Debian (chromium and libxslt), Fedora (chromium, expat, libssh, and webkitgtk), Oracle (avahi, firefox, ImageMagick, kernel, libtpms, and mysql), Red Hat (kernel), SUSE (bird3, expat, kernel, and tiff), and Ubuntu (dpkg, gnuplot, linux, linux-aws, linux-aws-5.15, linux-gcp, linux-gcp-5.15, linux-gke, linux-gkeop, linux-hwe-5.15, linux-ibm, linux-ibm-5.15, linux-intel-iotg, linux-intel-iotg-5.15, linux-lowlatency, linux-lowlatency-hwe-5.15, linux-nvidia, linux-nvidia-tegra, linux-nvidia-tegra-5.15, linux-oracle, linux-raspi, linux-riscv-5.15, linux-xilinx-zynqmp, linux, linux-aws, linux-gcp, linux-gcp-6.14, linux-oracle, linux-realtime, linux-riscv, linux-riscv-6.14, linux-aws-fips, linux-fips, linux-gcp-fips, linux-azure, linux-azure-fips, linux-ibm, linux-ibm-6.8, linux-intel-iot-realtime, linux-realtime, linux-oem-6.14, linux-oracle-5.15, linux-realtime-6.14, and python-eventlet).

Version 18 of the PostgreSQL database has been released. Notable improvements in this release include "skip scan" lookups for multicolumn B-tree indexes, virtual generated columns, better text processing, oauth authentication, and a new asynchronous I/O (AIO) subsystem to improve performance:

AIO lets PostgreSQL issue multiple I/O requests concurrently instead of waiting for each to finish in sequence. This expands existing readahead and improves overall throughput. AIO operations supported in PostgreSQL 18 include sequential scans, bitmap heap scans, and vacuum. Benchmarking has demonstrated performance gains of up to 3x in certain scenarios.

There are, of course, many other improvements and changes; see the release notes for full details.

Inside this week's LWN.net Weekly Edition:

• Front: Debian stable bug; Canceling async Rust; CHERI Linux; Time-slice extension; Multikernel; Revocable references; Blender 4.5.
• Briefs: Bluefin LTS; RPM 6.0.0; Tails 7.0; Rust 1.90.0; Infrastructure costs; Quotes; ...
• Announcements: Newsletters, conferences, security updates, patches, and more.

Asynchronous Rust code has what Rain Paharia calls a "universal cancellation protocol", meaning that any asynchronous code can be interrupted in the same way. They claim that this is both a useful feature when used deliberately, and a source of errors when done by accident. They presented about this problem at RustConf 2025, offering a handful of techniques to avoid introducing bugs into asynchronous Rust code.

The Capability Hardware Enhanced RISC Instructions (CHERI) project is a rethinking of computer architecture in order to improve system security. Carl Shaw gave a presentation at Linux Security Summit Europe (LSS EU) about CHERI and the efforts to get Linux running on it. He introduced capabilities, which are a mechanism for access control, and outlined their history, which goes back many decades at this point, then looked more specifically at the CHERI project and what it will take to apply the security constraints of capabilities to an operating system like Linux.

Security updates have been issued by AlmaLinux (kernel and kernel-rt), Fedora (expat), Red Hat (kernel and multiple packages), SUSE (avahi, busybox, busybox-links, kernel, sevctl, tcpreplay, thunderbird, and tor), and Ubuntu (isc-kea, linux, linux-aws, linux-gcp, linux-gke, linux-gkeop, linux-lowlatency, linux-lowlatency-hwe-6.8, linux-aws-6.8, linux-gcp-6.8, linux-aws-fips, linux-nvidia, linux-nvidia-6.8, linux-nvidia-lowlatency, linux-realtime, python-pip, and rabbitmq-server).

The Open Source Security Foundation (OpenSSF) has put together a joint statement from many of the public package repositories for various languages about the need for assistance in maintaining these commons. Services such as PyPI for Python, crates.io for Rust, and many others are working together to try to find ways to sustain these services in the face of challenges from "automated CI systems, large-scale dependency scanners, and ephemeral container builds" all downloading enormous amounts of package data, coupled with the rise of generative and agentic AI "driving a further explosion of machine-driven, often wasteful automated usage, compounding the existing challenges". It is not a crisis, yet, they say, but it is headed in that direction. Despite serving billions (perhaps even trillions) of downloads each month (largely driven by commercial-scale consumption), many of these services are funded by a small group of benefactors. Sometimes they are supported by commercial vendors, such as Sonatype (Maven Central), GitHub (npm) or Microsoft (NuGet). At other times, they are supported by nonprofit foundations that rely on grants, donations, and sponsorships to cover their maintenance, operation, and staffing.

Regardless of the operating model, the pattern remains the same: a small number of organizations absorb the majority of infrastructure costs, while the overwhelming majority of large-scale users, including commercial entities that generate demand and extract economic value, consume these services without contributing to their sustainability.

A bug in a recent release of systemd's network manager caused headaches for people managing systems that have a virtual LAN (VLAN) interface on a bridge; something one might want to do, for example, when configuring network interfaces for virtual machines. The bug affected several Debian users when upgrading the systemd package from v257.7-1 to v257.8-1. The updated package is part of the Debian 13.1 release, and the bug has snared enough users to cause a minor stir—due in no small part to the maintainer's response as much as the bug itself.

Security updates have been issued by Debian (corosync and kernel), Fedora (checkpointctl, chromium, curl, and perl-Catalyst-Authentication-Credential-HTTP), SUSE (firefox, frr, kernel, rustup, vim, and wireshark), and Ubuntu (glibc and pam).

Version 6.0.0 of the RPM Package Manager has been released. Notable changes in this release include support for multiple OpenPGP signatures per package, the ability to update previously installed PGP keys, as well as support for RPM v4 and v6 packages. See the release notes for full details.

Computers were once relatively static devices; if a peripheral was present at boot, it was unlikely to disappear while the system was operating. Those days are far behind us, though; devices can come and go at any time, often with no notice. That impermanence can create challenges for kernel code, which may not be expecting resources it is managing to make an abrupt exit. The revocable resource management patch set from Tzung-Bi Shih is meant to help with the creation of more robust — and more secure — kernel subsystems in a dynamic world.

Security updates have been issued by Debian (ffmpeg, jetty12, jetty9, jq, and pam), Fedora (curl, libssh, podman-tui, and prometheus-podman-exporter), Oracle (firefox, gnutls, kernel, and thunderbird), and SUSE (bluez, cairo, chromium, cmake, cups, firefox, frr, govulncheck-vulndb, kernel, kubevirt, virt-api-container, virt-controller-container, virt-exportproxy-container, virt-exportserver-container, virt-handler-container, virt-launcher-container, virt-libguestfs-t, mariadb, mybatis, ognl, python-h2, and rke2).

Linus has released 6.17-rc7 for testing. "Let's keep the testing going, and we'll have the final 6.17 in a week".

The Linux kernel generally wants to be in charge of the system as a whole; it runs on all of the available CPUs and controls access to them globally. Cong Wang has just come forward with a different approach: allowing each CPU to run its own kernel. The patch set is in an early form, but it gives a hint for what might be possible.