LWN on Kernel

posted by Roy Schestowitz on Jul 23, 2026

• LWN ☛ Lockless MPSC FIFO queues for io_uring

  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.

• LWN ☛ Topics in filesystem testing

  It should come as no surprise that a gathering of filesystem developers would discuss filesystem testing; it has been a mainstay of the Linux Storage, Filesystem, Memory Management, and BPF Summit over the years and the 2026 summit was no exception. Ted Ts'o led the discussion this time; he had a few different topics to raise, including his perception of increasing regressions for ext4 in the stable kernels and what can be done to help reduce them. As with other similar sessions at the summit over the years, there is a lot of interest in collaborating on test inputs and outputs, but finding a way to centralize that information has so far eluded the filesystem community.

  Ts'o began by noting that he has been noticing more ext4 regressions in the stable kernels of late. Part of the reason is that the ext4 developers have been working on features like support for folios; some of those patches ""have subtle dependency requirements that aren't necessarily getting picked up by the automation"".

• LWN ☛ Shielding running kernels against exploits with BPF

  Cisco has some unusual challenges when it comes to deploying security patches across the company's many devices running custom kernels. John Fastabend spoke about his work preventing exploits with BPF at the 2026 Linux Storage, Filesystem, Memory-Management, and BPF Summit. The technique could substantially reduce the time necessary to respond to kernel vulnerabilities, but it will not be fully effective unless more hooks are added to the kernel.

  Network switches encompass a big range of hardware, Fastabend began. From small single-rack systems all of the way through huge high-speed devices. Each of Cisco's supported platforms has its own kernel team that builds custom kernels using Yocto. At any given time, those teams are supporting a large number of different kernels — mostly stable kernels, fortunately, he added. All of these widely deployed, internet-connected devices with custom kernels make tempting targets for attackers.

• LWN ☛ Sending packets directly from BPF

  Tetragon, the BPF-based security monitoring tool, uses BPF to monitor different aspects of a running kernel and enforce user-specified policies. It sends its data to a user-space process, which forwards the data to a central monitoring service elsewhere in the network, however. This presents a point of vulnerability: if an attacker can kill Tetragon's user-space agent, it won't be able to properly report on the situation. Song Liu, Mahé Tardy, and Liam Wiseheart spoke about their work removing the need for the user-space agent at the 2026 Linux Storage, Filesystem, Memory-Management, and BPF Summit.

  Wiseheart clarified that he works at Meta, not on Tetragon, but he has an interest in solving the same problem of allowing BPF programs to run entirely disconnected from any user-space components. Currently, Meta takes the approach of pinning programs at system boot time, which at least prevents the programs from being removed if the user-space components are killed, but doesn't completely avoid the problem.