NVIDIA interview questions

Phone interview for 15 min: Three questions; 1. What is Volatile variable 2. How would you implement mutex 3. Struct and unions

I was directly interviewed by the hiring Manager. It was 1:1 interview and it began with my current job description and past experience. I was given a scan chain shifting problem on board and interviewer asked me to explain the reason of failure and where can be the failure. As far as I believe my analysis was right but interviewer did not look convinced.