Hi! On !PREEMPT_RT systems, printk-ing on a CPU that is coming online can produce a nasty illegal RCU usage splat [0]. To fix this, use the correct RCU API in rcuwait_has_sleeper(), as seen in Torvalds' tree at 76f258bf3f2aa. I have appended a patch with a more detailed commit message. Thanks, Derek [0] https://lore.kernel.org/linux-rt-users/5x4nejpojrtny37k7l6loewqwuaituq77zc3tkkojvawcuvmml@thwg65fdb3vn/
