On 15.08.24 10:04, Alice Ryhl wrote: > On Thu, Aug 15, 2024 at 9:49 AM Andreas Hindborg <nmi@xxxxxxxxxxxx> wrote: >> >> From: Andreas Hindborg <a.hindborg@xxxxxxxxxxx> >> >> When allocating `struct gendisk`, `GenDiskBuilder` is using a dynamic lock >> class key without registering the key. This is incorrect use of the API, >> which causes a `WARN` trace. This patch fixes the issue by using a static >> lock class key, which is more appropriate for the situation anyway. >> >> Fixes: 3253aba3408a ("rust: block: introduce `kernel::block::mq` module") >> Reported-by: "Behme Dirk (XC-CP/ESB5)" <Dirk.Behme@xxxxxxxxxxxx> >> Closes: https://rust-for-linux.zulipchat.com/#narrow/stream/288089-General/topic/6.2E11.2E0-rc1.3A.20rust.2Fkernel.2Fblock.2Fmq.2Ers.3A.20doctest.20lock.20warning >> Signed-off-by: Andreas Hindborg <a.hindborg@xxxxxxxxxxx> > > LGTM. This makes me wonder if there's some design mistake in how we > handle lock classes in Rust. So `LockClassKey::new` doesn't initialize the `lock_class_key` and is also movable. I think in this case we either just overlooked it or thought that the C side would initialize it. For those people that know about this, are there APIs that initialize `lock_class_key` themselves? (ie not a function to initialize a lock class key, but rather an API like `__blk_mq_alloc_disk`) Because if it is usually expected that the class key is already initialized, then I think we should change our abstraction. Additionally, I think that it needs to be pinned, since it contains an `struct hlist_node` (I might be wrong on this, but that looks and sounds like an intrusive linked list). Also the `new` function is probably prone for misuse, since it will create a new lock class key every time it is run. But as I learned in [1], the more common use-case is a single lock class key for several locks. Therefore it might be a good idea to at least rename it to `new_dynamic` or similar and add appropriate documentation pointing to `static_lock_class!`. [1]: https://rust-for-linux.zulipchat.com/#narrow/stream/288089-General/topic/.E2.9C.94.206.2E11.2E0-rc1.3A.20rust.2Fkernel.2Fblock.2Fmq.2Ers.3A.20doctest.20lock.20warning/near/460074755 --- Cheers, Benno