On Wednesday, November 30th, 2022 at 16:23, André Almeida <andrealmeid@xxxxxxxxxx> wrote: > On 11/28/22 06:30, Simon Ser wrote: > > > The PID is racy, the user-space daemon could end up killing an > > unrelated process… Is there any way we could use a pidfd instead? > > Is the PID race condition something that really happens or rather > something theoretical? A PID race can happen in practice if many PIDs get spawned. On Linux PIDs wrap around pretty quickly. Note, even a sandboxed program inside its own PID namespace can trigger the wrap-around. > Anyway, I can't see how pidfd and uevent would work together. Since > uevent it's kind of a broadcast and pidfd is an anon file, it wouldn't > be possible to say to userspace which is the fd to be used giving that > file descriptors are per process resources. Yeah, I can see how this can be difficult to integrate with uevent. > On the other hand, this interface could be converted to be an ioctl that > userspace would block waiting for a reset notification, then the kernel > could create a pidfd and give to the blocked process the right fd. We > would probably need a queue to make sure no event is lost. A blocking IOCTL wouldn't be very nice, you can't integrate that into an event loop for instance…
