Kernel quality control, or the lack thereof

Especially in my part of the Linux kernel, there is great value in preventing problems from reaching the -tip tree, let alone Linus's tree, let alone distributions, let alone customers. This great value stems from the fact that RCU bugs tend to be a bit difficult to reproduce and track down. It is therefore quite important to test the common cases.

Nevertheless, your last sentence is spot on. It is precisely because rcutorture forces rare code paths and rare race conditions to execute more frequently that the number of RCU bugs reaching customers is kept down to a dull roar.