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Historically, context tracking had to deal with fragile entry code path, ie: before user_exit() is called and after user_enter() is called, in case some of those spots would call schedule() or use RCU. On such cases, the site had to be protected between exception_enter() and exception_exit() that save the context tracking state in the task stack. Such sleepable fragile code path had many different origins: tracing, exceptions, early or late calls to context tracking on syscalls... Aside of that not being pretty, saving the context tracking state on the task stack forces us to run context tracking on all CPUs, including housekeepers, and prevents us to completely shutdown nohz_full at runtime on a CPU in the future as context tracking and its overhead would still need to run system wide. Now thanks to the extensive efforts to sanitize x86 entry code, those conditions have been removed and we can now get rid of these workarounds in this architecture. Create a Kconfig feature to express this achievement. Signed-off-by: Frederic Weisbecker <frederic@kernel.org> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://lkml.kernel.org/r/20201117151637.259084-2-frederic@kernel.org |
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