On Wed, Feb 12, 2020 at 1:48 PM Eric W. Biederman <ebiederm@xxxxxxxxxxxx> wrote: > > The good news is proc_flush_task isn't exactly called from process exit. > proc_flush_task is called during zombie clean up. AKA release_task. Yeah, that at least avoids some of the nasty locking while dying debug problems. But the one I was more worried about was actually the lock contention issue with lots of processes. The lock is basically a single global lock in many situations - yes, it's technically per-ns, but in a lot of cases you really only have one namespace anyway. And we've had problems with global locks in this area before, notably the one you call out: > Further after proc_flush_task does it's thing the code goes > and does "write_lock_irq(&task_list_lock);" Yeah, so it's not introducing a new issue, but it is potentially making something we already know is bad even worse. > What would be downside of having a mutex for a list of proc superblocks? > A mutex that is taken for both reading and writing the list. That's what the original patch actually was, and I was hoping we could avoid that thing. An rwsem would be possibly better, since most cases by far are likely about reading. And yes, I'm very aware of the task_list_lock, but it's literally why I don't want to make a new one. I'm _hoping_ we can some day come up with something better than task_list_lock. Linus