> Why not have context switches write to ringBuffer1 and sampling events write to ringBuffer2 (i.e. use different ringBuffers)

That would work, but at the cost of doubling memory usage, since you then have two fixed-size ring buffers instead of one. Also, in our particular cases, the correct ordering of events is important, which is ~automatic with a single ring buffer, but gets much trickier with two.

> This way buggy kernels should work properly too !?

We have a workaround for older/buggy kernels in place. We simply guard against same-CPU recursion by maintaining per-CPU state that indicates whether a given CPU is currently in the process of adding data to the ring buffer. If that state is set, we discard events, which prevents the recursion too.