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[$] Preventing atomic-context violations in Rust code with klint
One of the core constraints when programming in the kernel is the need to avoid sleeping when running in atomic context. For the most part, the responsibility for adherence to this rule is placed on the developer's shoulders; Rust developers, though, want the compiler to ensure that code is safe whenever possible. At the 2023 Linux Plumbers Conference, Gary Guo presented (via a remote link) the klint tool, which can find and flag many atomic-context violations before they turn into user-affecting bugs.
[$] The real realtime preemption end game
The addition of realtime support to Linux is a long story; it first shows up in LWN in 2004. For much of that time, it has seemed like only a little more work was needed to get across the finish line; thus we ran headlines like the realtime preemption endgame — in 2009. At the 2023 Linux Plumbers Conference, Thomas Gleixner informed the group that, now, the end truly is near. There is really only one big problem left to be solved before all of that work can land in the mainline.
[$] LWN.net Weekly Edition for November 16, 2023
Posted Nov 16, 2023 2:41 UTC (Thu)The LWN.net Weekly Edition for November 16, 2023 is available.
Inside this week's LWN.net Weekly Edition
- Front: Virtme-ng; Saving Itanium; listmount() and statmount(); 6.7 Merge window; Common Lisp in Emacs.
- Briefs: Reptar; Linux 6.7-rc1; eBPF documentary; GCC COBOL; ...
- Announcements: Newsletters, conferences, security updates, patches, and more.
[$] Faster kernel testing with virtme-ng
Building new kernels and booting into them is an unavoidable—and time-consuming—part of kernel development. Andrea Righi works for Canonical on the Ubuntu kernel team, so he does a lot of that and wanted to find a way to speed up the task. To that end, he has been working on virtme-ng, which is a way to boot a new kernel in a virtual machine, and it does so quickly. He came to the 2023 Linux Plumbers Conference (LPC) in Richmond, Virginia to introduce the project to a wider audience.
[$] Using Common Lisp in Emacs
Lisp is one of the oldest programming languages still in use today, but it has evolved in multiple directions over its more than 60-year history. Two of the more prominent descendants, Common Lisp and Emacs Lisp (or Elisp), are fairly closely related at some level, but there is still something of a divide between them. Some recent discussion in the emacs-devel mailing list have shown that some elements from Common Lisp are not completely welcome in Elisp—at least in the code that is maintained by the Emacs project itself.
[$] The rest of the 6.7 merge window
By the time that the 6.7 merge window closed on November 12, 15,418 non-merge changesets had been pulled into the mainline kernel. That makes this one of the busiest merge windows ever; if one discounts the lengthy bcachefs development history (some 2,800 commits), though, then the patch volume is roughly in line with other recent kernels. Over 5,000 of those commits were merged after our first-half merge-window summary was written.
[$] listmount() and statmount()
Years ago, the list of mounted filesystems on a Unix or Linux machine was relatively short and static. Adding a filesystem, which typically involved buying a new drive, happened rarely. In contrast, contemporary systems with a large number of containers can have a long and dynamic list of mounted filesystems. As was discussed at the 2023 LSFMM+BPF Summit, the Linux kernel's mechanism for providing information about mounted filesystems has not kept up with this change, leading to system-management headaches. Now, two new system calls proposed by Miklos Szeredi look set to provide some much-needed pain relief.
[$] The push to save Itanium
It is (relatively) easy to add code to the kernel; it tends to be much harder to remove that code later. The most recent example of this dynamic can be seen in the story of the ia64 ("Itanium") architecture, support for which was removed during the 6.7 merge window. That removal has left a small group of dedicated ia64 users unhappy and clinging to a faint hope that this support could return in a year's time.
LWN.net Weekly Edition for November 9, 2023
Posted Nov 9, 2023 0:06 UTC (Thu)The LWN.net Weekly Edition for November 9, 2023 is available.
Inside this week's LWN.net Weekly Edition
- Front: Patches on linux-kernel; Guest-first memory; 6.7 Merge window; BPF network device; Python C API.
- Briefs: Openwall sponsorship; Fedora 39; OpenELA; Ubuntu Core Desktop; Gawk 5.3; Home Assistant 2023.11; Quotes; ...
- Announcements: Newsletters, conferences, security updates, patches, and more.
Reducing patch postings to linux-kernel
The linux-kernel mailing list famously gets an enormous amount of email on a daily basis; the volume is so high that various email providers try to rate-limit it, which can lead to huge backlogs on the sending side and, of course, delayed mail. Part of the reason there is so much traffic is that nearly every patch gets copied to the mailing list, even when it may be unnecessary to do so. A proposed change would start shunting some of that patch email aside and, as might be guessed, has both supporters and detractors, but the discussion does highlight some of the different ways the mailing list is used by kernel developers.
Security updates for Friday
Security updates have been issued by Debian (webkit2gtk), Fedora (microcode_ctl, pack, and tigervnc), Slackware (gimp), SUSE (frr, gcc13, go1.20, go1.20-openssl, go1.21, go1.21-openssl, libnbd, libxml2, python-Pillow, python-urllib3, and xen), and Ubuntu (intel-microcode and openvpn).
Rust 1.74.0 released
Version 1.74.0 of the Rust language has been released. New features include better configuration for linters, authenticated cargo repositories, and support for projections in opaque return types.
Security updates for Thursday
Security updates have been issued by Debian (chromium and openvpn), Oracle (kernel, microcode_ctl, plexus-archiver, and python), Red Hat (.NET 6.0, dotnet6.0, dotnet7.0, dotnet8.0, kernel, linux-firmware, and open-vm-tools), SUSE (apache2, chromium, jhead, postgresql12, postgresql13, and qemu), and Ubuntu (dotnet6, dotnet7, dotnet8, frr, python-pip, quagga, and tidy-html5).
Intel's "redundant prefix issue"
Tavis Ormandy has described a bug in some Intel CPUs that can lead to a crash (or worse):
We believe this bug causes the frontend to miscalculate the size of the movsb instruction, causing subsequent entries in the ROB [reorder buffer] to be associated with incorrect addresses. When this happens, the CPU enters a confused state that causes the instruction pointer to be miscalculated.The machine can eventually recover from this state, perhaps with incorrect intermediate results, but becoming internally consistent again. However, if we cause multiple SMT or SMP cores to enter the state simultaneously, we can cause enough microarchitectural state corruption to force a machine check.
Intel has released a microcode update to address the issue.
A GNU COBOL status update
For the COBOL users out there, James K. Lowden has posted an update on the current status of the GNU COBOL compiler.
When in November we turn back our clocks, then naturally do programmers' thoughts turn to Cobol, its promise, and future.At last post, nine months ago, we were working our way through the NIST CCVS/85 test suite. I am pleased to report that process is complete. As far as NIST is concerned, gcobol is a Cobol compiler.
Security updates for Wednesday
Security updates have been issued by Debian (libclamunrar and ruby-sanitize), Fedora (frr, roundcubemail, and webkitgtk), Mageia (freerdp and tomcat), Red Hat (avahi, bind, c-ares, cloud-init, container-tools:4.0, container-tools:rhel8, cups, dnsmasq, edk2, emacs, flatpak, fwupd, ghostscript, grafana, java-21-openjdk, kernel, kernel-rt, libfastjson, libmicrohttpd, libpq, librabbitmq, libreoffice, libreswan, libX11, linux-firmware, mod_auth_openidc:2.3, nodejs:20, opensc, perl-HTTP-Tiny, procps-ng, protobuf-c, python-cryptography, python-pip, python27:2.7, python3, python3.11, python3.11-pip, python38:3.8, python38-devel:3.8, python39:3.9, python39-devel:3.9, qt5-qtbase, qt5-qtsvg, rhc, ruby:2.5, shadow-utils, squid:4, sysstat, tang, tomcat, tpm2-tss, virt:rhel, virt-devel:rhel, webkit2gtk3, wireshark, xorg-x11-server, xorg-x11-server-Xwayland, and yajl), Slackware (mariadb), SUSE (chromium, connman, exfatprogs, ucode-intel, and w3m), and Ubuntu (cobbler, ffmpeg, linux-oem-6.5, procps, and traceroute).
Security updates for Tuesday
Security updates have been issued by Debian (postgresql-11, postgresql-13, and postgresql-15), Fedora (chromium, optipng, and radare2), Scientific Linux (plexus-archiver and python), Slackware (tigervnc), SUSE (apache2, containerized-data-importer, kernel-firmware-nvidia-gspx-G06, nvidia-open- driver-G06-signed, postgresql, postgresql15, postgresql16, postgresql12, postgresql13, python-Django1, squashfs, and xterm), and Ubuntu (firefox and memcached).
Security updates for Monday
Security updates have been issued by Debian (audiofile and ffmpeg), Fedora (keylime, python-pillow, and tigervnc), Mageia (quictls and vorbis-tools), Oracle (grub2), Red Hat (galera, mariadb, plexus-archiver, python, squid, and squid34), and SUSE (clamav, kernel, mupdf, postgresql14, tomcat, tor, and vlc).
Kernel prepatch 6.7-rc1
Linus Torvalds has released 6.7-rc1, thus closing the merge window for this release. It is the largest merge window ever, but some of that was due to the bcachefs history that came with merge of that filesystem.
But 6.7 is pretty big in other ways too, with12678 files changed, 838819 insertions(+), 280754 deletions(-)
which is also bigger than those historically big releases [4.9, 5.8 and 5.13]. And that's not due to bcachefs, that's actually mainly due to ia64 removal and a lot of GPU support (notably lots of AMD GPU header files again - lots and lots of lines, but there's support for new nvidia cards too).
A documentary on the development of eBPF
For folks with an interest in how extended BPF came to be and a half-hour to spare, the announcement has gone out of a new film called "eBPF: Unlocking the kernel", released at the KubeCon+CloudNativeCon event. The documentary is available on YouTube.