On Mon, Jan 13, 2025 at 5:49 PM Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote: > > On Mon, 13 Jan 2025 12:14:19 +0000 Lorenzo Stoakes <lorenzo.stoakes@xxxxxxxxxx> wrote: > > > A nit on subject, I mean this is part of what this series does, and hey - > > we have only so much text to put in here - but isn't this both > > reimplementing per-VMA lock as a refcount _and_ importantly allocating VMAs > > using the RCU typesafe mechanism? > > > > Do we have to do both in one series? Can we split this out? I mean maybe > > that's just churny and unnecessary, but to me this series is 'allocate VMAs > > RCU safe and refcount VMA lock' or something like this. Maybe this is > > nitty... but still :) > > > > One general comment here - this is a really major change in how this stuff > > works, and yet I don't see any tests anywhere in the series. > > > > I know it's tricky to write tests for this, but the new VMA testing > > environment should make it possible to test a _lot_ more than we previously > > could. > > > > However due to some (*ahem*) interesting distribution of where functions > > are, most notably stuff in kernel/fork.c, I guess we can't test > > _everything_ there effectively. > > > > But I do feel like we should be able to do better than having absolutely no > > testing added for this? > > > > I think there's definitely quite a bit you could test now, at least in > > asserting fundamentals in tools/testing/vma/vma.c. > > > > This can cover at least detached state asserts in various scenarios. > > > > But that won't cover off the really gnarly stuff here around RCU slab > > allocation, and determining precisely how to test that in a sensible way is > > maybe less clear. > > > > But I'd like to see _something_ here please, this is more or less > > fundamentally changing how all VMAs are allocated and to just have nothing > > feels unfortunate. > > > > I'm already nervous because we've hit issues coming up to v9 and we're not > > 100% sure if a recent syzkaller is related to these changes or not, I'm not > > sure how much we can get assurances with tests but I'd like something. > > Thanks. > > Yes, we're at -rc7 and this series is rather in panic mode and it seems > unnecessarily risky so I'm inclined to set it aside for this cycle. > > If the series is considered super desirable and if people are confident > that we can address any remaining glitches during two months of -rc > then sure, we could push the envelope a bit. But I don't believe this > is the case so I'm thinking let's give ourselves another cycle to get > this all sorted out? I didn't think this series was in panic mode with one real issue that is not hard to address (memory ordering in __refcount_inc_not_zero_limited()) but I'm obviously biased and might be missing the big picture. In any case, if it makes people nervous I have no objections to your plan. Thanks, Suren.
