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Bringing restartable sequences out of the niche
The restartable sequences feature, which was added to the 4.18 kernel in 2018, exists to enable [...]
It makes obvious sense to tie a feature like this to restartable sequences, so the time-slice-extension patch set added the "please can I run a little longer" bit to the shared area. The restartable-sequences code in current kernels maintains a field, rseq_event_mask, in each thread's task_struct structure to track those ways; there are separate bits for preemption, the delivery of a signal, and migration to a different CPU. When running on a kernel built with the DEBUG_RSEQ configuration option, making a system call while in a critical section will result in the immediate termination of the offending process — a gentle hint that the restartable sequences feature is not being used correctly.
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