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

[Tetsuo Handa]

On 2026/06/19 18:49, Andreas Hindborg wrote:
>> My understanding is that we don't have infrastructure for lock class keys
>> that can be applied to
>>
>>   +struct gendisk_lkclass {
>>   +	struct lock_class_key bio_lkclass;
>>   +	struct lock_class_key open_mutex_lkclass;
>>   +};
>>
>>   -	static struct lock_class_key __key;
>>   +	static struct gendisk_lkclass __key;
>>
>> change. Alternative approach is welcomed if you have one.
> 
> Sorry, I did not pay enough attention. I would suggest this approach:

I'm OK with your module-specific lockdep class approach

> @@ -164,14 +127,21 @@ pub fn build<T: Operations>(
>              lim.features = bindings::BLK_FEAT_ROTATIONAL;
>          }
>  
> -        // SAFETY: `tagset.raw_tag_set()` points to a valid and initialized tag set
> +        let keys = KBox::pin_init(
> +            Opaque::ffi_init(|ptr: *mut bindings::gendisk_lkclass| {
> +                // SAFETY: `ptr` is valid for writes
> +                unsafe { bindings::lockdep_register_key(&raw mut (*ptr).bio_lkclass) };
> +                // SAFETY: `ptr` is valid for writes
> +                unsafe { bindings::lockdep_register_key(&raw mut (*ptr).open_mutex_lkclass) };
> +            }),
> +            GFP_KERNEL,
> +        )?;
> +
> +        // SAFETY:
> +        // - `tagset.raw_tag_set()` points to a valid and initialized tag set.
> +        // - We keep `keys` alive for the lifetime of the returned gendisk.
>          let gendisk = from_err_ptr(unsafe {
> -            bindings::__blk_mq_alloc_disk(
> -                tagset.raw_tag_set(),
> -                &mut lim,
> -                data,
> -                lkclass.as_ptr(),
> -            )
> +            bindings::__blk_mq_alloc_disk(tagset.raw_tag_set(), &mut lim, data, keys.get())
>          })?;
>  
>          const TABLE: bindings::block_device_operations = bindings::block_device_operations {

if we can assume that there is (up to) only one

  let mut disk = gen_disk::GenDiskBuilder::new().capacity_sectors(4096).build(fmt!("myblk"), tagset, ())?;

call for each rust module.

By the way, are you aware that rust-enabled linux-next build is recently failing
( https://syzkaller.appspot.com/bug?extid=1f14a35d0c73d31555e4 ) ?