Including <linux/bit_spinlock.h> into an empty TU will result in the compiler complaining: ./include/linux/bit_spinlock.h:34:4: error: call to undeclared function 'cpu_relax'; <...> 34 | cpu_relax(); | ^ 1 error generated. Include <asm/processor.h> to allow including bit_spinlock.h where <asm/processor.h> is not otherwise included. Signed-off-by: Marco Elver <elver@xxxxxxxxxx> --- include/linux/bit_spinlock.h | 2 ++ 1 file changed, 2 insertions(+) diff --git a/include/linux/bit_spinlock.h b/include/linux/bit_spinlock.h index bbc4730a6505..f1174a2fcc4d 100644 --- a/include/linux/bit_spinlock.h +++ b/include/linux/bit_spinlock.h @@ -7,6 +7,8 @@ #include <linux/atomic.h> #include <linux/bug.h> +#include <asm/processor.h> /* for cpu_relax() */ + /* * bit-based spin_lock() * -- 2.48.1.502.g6dc24dfdaf-goog