Re: [PATCH v3] block: assign caller-specific lockdep class to disk->open_mutex

[Andreas Hindborg <a.hindborg@kernel.org>]

Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> writes:

> The block core currently allocates a single monolithic lockdep key for
> disk->open_mutex across all callers. This single key conflates locking
> hierarchies between independent block streams. For example, if a stacked
> driver like loop flushes its internal workqueues inside lo_release() while
> holding its own open_mutex, lockdep views this as a potential ABBA deadlock
> against the underlying storage stack, leading to numerous circular
> dependency splats.
>
> To structurally reduce false positives, this patch splits the global
> monolithic lock class into distinct, per-caller instances during disk
> allocation. This is done by replacing "struct lock_class_key" with
> "struct gendisk_lkclass", which contains two instances of
> "struct lock_class_key" for the legacy "(bio completion)" map and
> disk->open_mutex respectively.
>
> Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>

For the Rust part, we have existing infrastructure for lock class keys
[1]. Please take a look how we generate lock class keys elsewhere [2].

Best regards,
Andreas Hindborg

[1] https://rust.docs.kernel.org/kernel/sync/struct.LockClassKey.html
[2] https://github.com/torvalds/linux/blob/ddd664bbff63e09e7a7f9acae9c43605d4cf185f/rust/kernel/sync/lock/mutex.rs#L12