On Mon, Feb 17, 2025 at 02:20:57PM +0100, Martin Pieuchot wrote: > On 17/02/25(Mon) 03:16, Claudio Jeker wrote: > > CVSROOT: /cvs > > Module name: src > > Changes by: clau...@cvs.openbsd.org 2025/02/17 03:16:05 > > > > Modified files: > > sys/kern : kern_exit.c > > > > Log message: > > Use ps_mtx to lock the child process that is being checked by dowait6. > > > > The checks of the various ps_flags field is all but atomic so we need > > to lock the process before doing all these checks. Only that way a > > reliable result is seen. It also ensures that the child process did > > finish the transition before signaling up to the parent. > > Why not read `ps_flags' only once?
We could do that. Will it help, not sure. I fought enough with dowait6() and just want to be sure to not trip over it all the time. > Anyway I don't understand what is being protected here. It is really > hard to follow without documentation. Can you tells us which fields > you're serializing access with `ps_mtx' in sys/proc.h? > > This should be like the manual rule. Locking MUST BE documented. The problem is that the atomic flags are not atomic with the process state. So right now I prefer to use a mutex and make sure that there are no concurrency issues. The wait process wants to inspect the current state of a process and to do that it should hold the ps_mtx so that the state is stable. This is mainly for stop and continue signaling, exit is a different beast but will also require this in the long run. How do you want this documented? -- :wq Claudio
