Sometimes my pinky finger locks up while I'm playing. It's never painful, but always annoying. It happens when I stretch it out straight, applying a lot of pressure at the tip, like when I'm doing rolls on the 5th and 6th strings. Then it gets stuck. I can't bend it back to a normal playing position until I take all my fingers off the fretboard and flex them backwards. This can be problematic if I'm trying to play without pausing.

It occurred to me today that it might be happening less often. If so, I credit the way I've been practicing arpeggios. To avoid the habit of running straight up and down scales or arpeggios when improvising, I like to practice in sequences instead. The easiest one is to skip a note, then play the skipped note. In a scale, you'd play 1, 3, 2, 4, 3, 5, etc. In a 7th arpeggio, you'd play 1, 5, 3, 7, 5, 8, etc. This results in a lot of 4th intervals, which require finger rolls (same fret, same finger, adjacent strings) on most strings. I guess doing rolls with your pinky is a great way to strengthen it.