How would you fix signals and do you propose a complete set of patterns for safe concurrency? And so why is there limited scope for signal handlers?

Should you use signal handlers with eBPF?

It's not really possible to make them safer without hurting performance. Signals break the C virtual machine guarantees (atomics, memory consistency, register consistency, etc), and the only way to re-establish them for edge cases like signals would be to cripple the rest of the program with extra checks (basically making ALL data volatile).