news
LWN on Linux Kernel
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LWN ☛ Sched-ext: enqueue() for sub-schedulers and proxy-execution support [LWN.net]
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.
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LWN ☛ Debating the role of large language models in the kernel community [LWN.net]
Like many development communities, the kernel community has been struggling to determine how large language models (LLMs) 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.
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LWN ☛ Attaching programs to multiple tracepoints [LWN.net]
Tracepoints in the kernel are useful for a variety of purposes: debugging, active monitoring, and performance measurements, among other things. Previously, any given BPF program could only be attached to a single tracepoint. Jiri Olsa has been working to change that, and led a discussion about his progress at the 2026 Linux Storage, Filesystem, Memory-Management, and BPF Summit. That work has since been merged, and can be expected as part of the 7.2 kernel.
Other similar facilities in the kernel support multiple attachments; kprobes in particular support it, and can do most of the same things as tracepoints. The difference is one of performance, Olsa said. Tracepoints are slower to set up, but measurably faster to execute. His slides included measurements of how many millions of executions per second each method could manage. Depending on exactly how the tracepoint and kprobe are attached, tracepoints can be about twice as fast. If tracepoints could be made to support multiple attachment without a regression in performance, they would be an attractive option for monitoring performance-sensitive operations.
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LWN ☛ Securing BPF LSMs against tampering [LWN.net]
Since 2020, BPF programs have been able to act as Linux security modules (LSMs). Several projects, including systemd, have been working to use that capability to provide more security to users. Christian Brauner spoke at the 2026 Linux Storage, Filesystem, Memory-Management, and BPF Summit about some of the limitations of using BPF in this way, and the changes he would like to see for systemd's use. In particular, he would like a way to make sure that BPF programs cannot be removed or have their private data tampered with.
When a BPF program is attached to an LSM hook or other kernel resource, it is reference-counted: if the user-space program that submitted the BPF program to the kernel closes the file descriptor for the BPF program (for example, because it crashed), the BPF program is cleaned up automatically. This design keeps things tidy and prevents BPF programs from being leaked, but it exposes a point of vulnerability for BPF LSMs. In addition, it is often possible to interfere with a BPF program's execution by altering the data it has stored in BPF maps in unexpected ways. BPF maps are often used for communication with user-space programs, but they can also be used to store auxiliary data for the BPF program itself, and the BPF program can rely on the correctness of that data. Brauner would like to see both of these behaviors changed, so that BPF security programs, once installed, cannot be trivially circumvented.
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LWN ☛ Merging famfs? [LWN.net]
The famfs filesystem, which is meant to provide shared access to huge memory-resident files on CXL and other devices, returned to the Linux Storage, Filesystem, Memory Management, and BPF Summit (LSFMM+BPF) in 2026. It was first discussed at LSFMM+BPF 2024 and a new implementation was described at the 2025 gathering, but it still has not made its way into the kernel; LWN looked at a discussion about merging famfs back in April 2026.
John Groves began the session by noting that he is the creator and maintainer of famfs, which is the ""fabric-attached memory filesystem"". He works for Micron, which makes devices with large pools of memory that are accessible to multiple servers; those products are coming soon, though early access to them is available to some. There are some ""interesting management challenges"" for such devices and famfs is meant to allow Linux users to handle them. Since last year's summit, he has become the co-chair of the software and systems working group for the CXL Consortium; ""they had the bad judgment to elect me to that"", he said with a grin.