Linux Foundation, Kernel, and Linux Plumbers Conference
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Tech Giants Join Linux Foundation's Connected-Cities Efforts [Ed: Just surveillance capitalism inside Zemlin's PAC. Reminder: the spokesperson of the "Linux" Foundation is the former spokesperson of James Clapper.]
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Generalized events notification and security policies
Interfaces for the reporting of events to user space from the kernel have been a recurring topic on the kernel mailing lists for almost as long as the kernel has existed; LWN covered one 15 years ago, for example. Numerous special-purpose event-reporting APIs exist, but there are none that are designed to be a single place to obtain any type of event. David Howells is the latest to attempt to change that situation with a new notification interface that, naturally, uses a ring buffer to transfer events to user space without the need to make system calls. The API itself (which hasn't changed greatly since it was posted in 2018) is not hugely controversial, but the associated security model has inspired a few heated discussions.
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Detecting and handling split locks
The Intel architecture allows misaligned memory access in situations where other architectures (such as ARM or RISC-V) do not. One such situation is atomic operations on memory that is split across two cache lines. This feature is largely unknown, but its impact is even less so. It turns out that the performance and security impact can be significant, breaking realtime applications or allowing a rogue application to slow the system as a whole. Recently, Fenghua Yu has been working on detecting and fixing these issues in the split-lock patch set, which is currently on its eighth revision.
[...]
With a split lock, the value needs to be kept coherent between different CPUs, which means assuring that the two cache lines change together. As this is an uncommon operation, the hardware design needs to take a special path; as a result, split locks may have important consequences as described in the cover letter of Yu's patch set. Intel's choice was to lock the whole memory bus to solve the coherency problem; the processor locks the bus for the duration of the operation, meaning that no other CPUs or devices can access it. The split lock blocks not only the CPU performing the access, but also all others in the system. Configuring the bus-locking protocol itself also adds significant overhead to the system as a whole.
On the other hand, if the atomic operation operand fits into a single cache line, the processor will use a less expensive cache lock. This all means that developers may increase performance and avoid split locks by actions like simply correctly aligning their variables.
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Real-Time Microconference Accepted into 2019 Linux Plumbers Conference
We are pleased to announce that the Real-Time Microconference has been accepted into the 2019 Linux Plumbers Conference! The PREEMPT_RT patch set (aka “The Real-Time Patch”) was created in 2004 in the effort to make Linux into a hard real-time designed operating system. Over the years much of the RT patch has made it into mainline Linux, which includes: mutexes, lockdep, high-resolution timers, Ftrace, RCU_PREEMPT, priority inheritance, threaded interrupts and much more. There’s just a little left to get RT fully into mainline, and the light at the end of the tunnel is finally in view. It is expected that the RT patch will be in mainline within a year, which changes the topics of discussion. Once it is in Linus’s tree, a whole new set of issues must be handled. The focus on this year’s Plumbers events will include:
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Dilution and Misuse of the "Linux" Brand
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