[$] Toward race-free process signaling

Signals have existed in Unix systems for years, despite the general
consensus that they are an example of a bad
design
. Extensions and new ways of using signals pop up from time to
time, fixing the issues that have been found. A notable addition was the
introduction of signalfd()
nearly 10 years ago. Recently, the kernel developers have discussed how to avoid
race conditions related to process-ID (PID) recycling, which occurs when a
process
terminates and another one is assigned the same PID. A process that fails
to notice that its target has exited may try to send a signal to the wrong
recipient, with potentially grave consequences. A patch set from Christian
Brauner is trying to solve the issue by adding
signaling via file descriptors.

Source: LWN