On 2022-01-28 16:54:06 [+0100], Jason A. Donenfeld wrote: > Hi Sebastian, Hi Jason, > On Fri, Jan 28, 2022 at 4:44 PM Sebastian Andrzej Siewior > <bigeasy@xxxxxxxxxxxxx> wrote: > > NO. Could we please look at my RANDOM patches first? > > I can repost my rebased patched if there no objection. > > I did, and my reply is here: > https://lore.kernel.org/lkml/CAHmME9pzdXyD0oRYyCoVUSqqsA9h03-oR7kcNhJuPEcEMTJYgw@xxxxxxxxxxxxxx/ > > I was hoping for a series that addresses these issues. As I mentioned > before, I'm not super keen on deferring that processing in a > conditional case and having multiple entry ways into that same > functionality. I don't think that's worth it, especially if your > actual concern is just userspace calling RNDADDTOENTCNT too often > (which can be safely ratelimited). I don't think that thread needs to And what do you do in ratelimiting? As I explained, you get 20 that "enter" and the following are block. The first 20 are already problematic and you need a plan-B for those that can't enter. So I suggested a mutex_t around the ioctl() which would act as a rate limiting. You did not not follow up on that idea. > spill over here, though, so feel free to follow up with a v+1 on that > series and I'll happily take a look. Alternatively, if you'd like to > approach this by providing a patch for Jonathan's issue, that makes > sense too. So far, the things in front of me are: 1) your patchset > from last month that has unresolved issues, and 2) Andy's thing, which > maybe will solve the problem (or it won't?). A third alternative from > you would be most welcome too. I made a reply yesterday I think with some numbers yesterday. From my point of view it is an in-IRQ context/ code that can be avoided. The RNDADDTOENTCNT is a simple way to hammer on the lock and see how bad it gets. Things like add_hwgenerator_randomness() don't appear so often so it is hard to figure out what the worst case can be. Please ignore Jonathan report for now. As I tried to explain: This lockdep report shows a serious problem on PREEMPT_RT. There is _no_ need to be concerned on a non-PREEMPT_RT kernel. But it should be addressed. If this gets merged as-is then thanks to the stable tag it will get backported (again no change for !RT) and will collide with PREEMPT_RT patch. And as I mentioned, the locking is not working on PREEMPT_RT. > Jason Sebastian
