On Thu, Aug 15, 2024 at 08:07:38PM +0100, Gary Guo wrote: > On Thu, 15 Aug 2024 10:04:56 +0200 > Alice Ryhl <aliceryhl@xxxxxxxxxx> 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. > > > > Reviewed-by: Alice Ryhl <aliceryhl@xxxxxxxxxx> > > I agree. The API that we current have is designed without much > consideration into dynamically allocated keys, and we use `&'static > LockClassKey` in a lot of kernel crate APIs. > > This arguably is wrong, because presence of `&'static LockClassKey` > doesn't mean the key is static. If we do a > `Box::leak(Box::new(LockClassKey::new()))`, then this is a `&'static > LockClassKey`, but lockdep wouldn't consider this as a static object. > > Maybe we should make the `new` function unsafe. > I think a more proper fix is to make LockClassKey pin-init, for dynamically allocated LockClassKey, we just use lockdep_register_key() as the initializer and lockdep_unregister_key() as the desconstructor. And instead of a `&'static LockClassKey`, we should use `Pin<&'static LockClassKey>` to pass a lock class key. Of course we will need some special treatment on static allocated keys (e.g. assume they are initialized since lockdep doesn't require initialization for them). Pin initializer: impl LockClassKey { pub fn new() -> impl PinInit<Self> { pin_init!(Self { inner <- Opaque::ffi_init(|slot| { lockdep_register_key(slot) }) }) } } LockClassKey::new_uninit() for `static_lock_class!`: impl LockClassKey { pub const fn new_uninit() -> MaybeUninit<Self> { .... } } and the new `static_lock_class!`: macro_rules! static_lock_class { () => {{ static CLASS: MaybeUninit<$crate::sync::LockClassKey> = $crate::sync::LockClassKey::new_uninit(); // SAFETY: `CLASS` is pinned because it's static // allocated. And it's OK to assume it's initialized // because lockdep support uninitialized static // allocated key. unsafe { Pin::new_unchecked(CLASS.assume_init_ref()) } }}; } Thoughts? Regards, Boqun > For the patch itself: > > Reviewed-by: Gary Guo <gary@xxxxxxxxxxx>