lib: Add one-byte emulation function

2024-04-10T05:06:00+00:00

Architectures are required to provide four-byte cmpxchg() and 64-bit architectures are additionally required to provide eight-byte cmpxchg(). However, there are cases where one-byte cmpxchg() would be extremely useful. Therefore, provide cmpxchg_emu_u8() that emulates one-byte cmpxchg() in terms of four-byte cmpxchg(). Note that this emulations is fully ordered, and can (for example) cause one-byte cmpxchg_relaxed() to incur the overhead of full ordering. If this causes problems for a given architecture, that architecture is free to provide its own lighter-weight primitives. [ paulmck: Apply Marco Elver feedback. ] [ paulmck: Apply kernel test robot feedback. ] [ paulmck: Drop two-byte support per Arnd Bergmann feedback. ] Link: https://lore.kernel.org/all/0733eb10-5e7a-4450-9b8a-527b97c842ff@paulmck-laptop/ Signed-off-by: Paul E. McKenney Acked-by: Marco Elver Cc: Andrew Morton Cc: Thomas Gleixner Cc: "Peter Zijlstra (Intel)" Cc: Douglas Anderson Cc: Petr Mladek Cc: Arnd Bergmann Cc:

kernel/linux.git/include/linux/cmpxchg-emu.h, branch v6.18.21

lib: Add one-byte emulation function