My understanding of white knuckling means to be hanging on to anything through sheer determination, gritted teeth and a dash of luck, and being in danger of losing hold of it.
I grew up hearing this term referring to everything from roller coaster rides, to exams week, to visits from a mother in law.
It certainly described some time periods during early recovery, when I still had no idea what to do other than get wasted when things got hairy.
It still happens to me now in other areas of my life, and sometimes when I am stressed I actually wake up with my fists clenched so hard that my knuckles are literally white.