Re: [GIT PULL PATCH 0/9] Rust changes for v7.4-rc1

Re: [GIT PULL PATCH 0/9] Rust changes for v7.4-rc1

[Thorsten Leemhuis]

On 9/29/26 13:47, Jens Axboe wrote:
> On Tue, 29 Sep 2026 11:33:58 +0200, Andreas Hindborg wrote:
>> I have a number of Rust block layer patches I would ask you to pick for
>> v7.4. I have collected them into a patch series as well as a pull request
>> so you can use whatever is easier.
>>
>> The changes cover
>>
>>  - Style and formatting changes.
>>  - Documentation fixes.
>>  - Fixes for missing trait bounds that can cause API unsoundness.
>>  - A change to set the owner of the file operations vtable in `GenDisk`.
>>  - Two bug fixes for the rnull driver.
>>
>> [...]
> 
> Applied, thanks!
>  [...]

This series showed up in next today and broke the build for me on
various Fedora releases for aarch64 and x86_64; reverting this series
fixed that from a quick build test limited to drivers/block/rnull/

The full error msg is quote long, find the top of it below. Full log:
https://download.copr.fedorainfracloud.org/results/@kernel-vanilla/next/fedora-rawhide-aarch64/11055137-next-next-all/builder-live.log.gz

Ciao, Thorsten

"""
> error[E0277]: `UnsafeCell<MaybeUninit<blk_mq_tag_set>>` cannot be shared between threads safely
>    --> drivers/block/rnull/configfs.rs:57:18
>     |
>  57 |     type Child = DeviceConfig;
>     |                  ^^^^^^^^^^^^ `UnsafeCell<MaybeUninit<blk_mq_tag_set>>` cannot be shared between threads safely
>     |
>     = help: within `TagSet<NullBlkDevice>`, the trait `Sync` is not implemented for `UnsafeCell<MaybeUninit<blk_mq_tag_set>>`
> note: required because it appears within the type `Opaque<blk_mq_tag_set>`
>    --> rust/kernel/types.rs:332:12
>     |
> 332 | pub struct Opaque<T> {
>     |            ^^^^^^
> note: required because it appears within the type `TagSet<NullBlkDevice>`
>    --> rust/kernel/block/mq/tag_set.rs:32:12
>     |
>  32 | pub struct TagSet<T: Operations> {
>     |            ^^^^^^
>     = note: required for `Arc<TagSet<NullBlkDevice>>` to implement `Send`
>     = note: 1 redundant requirement hidden
>     = note: required for `GenDisk<NullBlkDevice>` to implement `Send`
> note: required because it appears within the type `Option<GenDisk<NullBlkDevice>>`
>    --> /usr/lib/rustlib/src/rust/library/core/src/option.rs:598:10
>     |
> 598 | pub enum Option<T> {
>     |          ^^^^^^
> note: required because it appears within the type `DeviceConfigInner`
>    --> drivers/block/rnull/configfs.rs:130:8
>     |
> 130 | struct DeviceConfigInner {
>     |        ^^^^^^^^^^^^^^^^^
>     = note: required for `Lock<DeviceConfigInner, MutexBackend>` to implement `Send`
> note: required because it appears within the type `DeviceConfig`
>    --> drivers/block/rnull/configfs.rs:124:19
>     |
> 124 | pub(crate) struct DeviceConfig {
>     |                   ^^^^^^^^^^^^
> note: required by a bound in `kernel::configfs::GroupOperations::Child`
>    --> rust/kernel/configfs.rs:518:27
>     |
> 518 |     type Child: 'static + Send;
>     |                           ^^^^ required by this bound in `GroupOperations::Child`
> 
> error[E0277]: `*const blk_mq_ops` cannot be sent between threads safely
>       --> drivers/block/rnull/configfs.rs:57:18
>        |
>     57 |     type Child = DeviceConfig;
>        |                  ^^^^^^^^^^^^ `*const blk_mq_ops` cannot be sent between threads safely
>        |
>        = help: within `TagSet<NullBlkDevice>`, the trait `Send` is not implemented for `*const blk_mq_ops`
> note: required because it appears within the type `blk_mq_tag_set`
>       --> /builddir/build/BUILD/kernel-7.3.0-build/kernel-next-20260930/linux-7.3.0-0.0.next.20260930.545.vanilla.fc46.aarch64/rust/bindings/bindings_generated.rs:105198:12
>        |
> 105198 | pub struct blk_mq_tag_set {
>        |            ^^^^^^^^^^^^^^
> note: required because it appears within the type `MaybeDangling<blk_mq_tag_set>`
>       --> /usr/lib/rustlib/src/rust/library/core/src/mem/maybe_dangling.rs:73:12
>        |
>     73 | pub struct MaybeDangling<P: ?Sized>(P);
> [...]"""

Re: [GIT PULL PATCH 0/9] Rust changes for v7.4-rc1

[Miguel Ojeda]

On Wed, Sep 30, 2026 at 5:07 PM Thorsten Leemhuis <linux@leemhuis.info> wrote:
>
> This series showed up in next today and broke the build for me on
> various Fedora releases for aarch64 and x86_64; reverting this series
> fixed that from a quick build test limited to drivers/block/rnull/
>
> The full error msg is quote long, find the top of it below. Full log:
> https://download.copr.fedorainfracloud.org/results/@kernel-vanilla/next/fedora-rawhide-aarch64/11055137-next-next-all/builder-live.log.gz

Confirmed, I see it e.g. in my arm32 build.

Cheers,
Miguel

Re: [GIT PULL PATCH 0/9] Rust changes for v7.4-rc1

[Gary Guo]

On Wed Sep 30, 2026 at 4:06 PM BST, Thorsten Leemhuis wrote:
> On 9/29/26 13:47, Jens Axboe wrote:
>> On Tue, 29 Sep 2026 11:33:58 +0200, Andreas Hindborg wrote:
>>> I have a number of Rust block layer patches I would ask you to pick for
>>> v7.4. I have collected them into a patch series as well as a pull request
>>> so you can use whatever is easier.
>>>
>>> The changes cover
>>>
>>>  - Style and formatting changes.
>>>  - Documentation fixes.
>>>  - Fixes for missing trait bounds that can cause API unsoundness.
>>>  - A change to set the owner of the file operations vtable in `GenDisk`.
>>>  - Two bug fixes for the rnull driver.
>>>
>>> [...]
>> 
>> Applied, thanks!
>>  [...]
>
> This series showed up in next today and broke the build for me on
> various Fedora releases for aarch64 and x86_64; reverting this series
> fixed that from a quick build test limited to drivers/block/rnull/
>
> The full error msg is quote long, find the top of it below. Full log:
> https://download.copr.fedorainfracloud.org/results/@kernel-vanilla/next/fedora-rawhide-aarch64/11055137-next-next-all/builder-live.log.gz

The `Child: Send` bound is introduced in configfs:
https://lore.kernel.org/all/tencent_05937A22D2DA2BAE808EF19E491AA109BC09@qq.com/.
So this is more or less a semantic conflict.

However, the fundamental issue is that TagSet never implements Send/Sync, which
means that "rust: block: fix `Send` bound for `GenDisk`" will unconditionally
strip away the Send implementation, which is problematic.

Something like this should fix the issue:

    unsafe impl<T: Operations<QueueData: Send>> Send for TagSet<T> {}
    unsafe impl<T: Operations<QueueData: Send>> Sync for TagSet<T> {}

That said, I am not sure why the GenDisk need to carry `Arc<TagSet<T>>: Send`
bound in the first place. Removing it should also fix the issue.

Also, the `QueueData: Send` bound should be part of the `Operations` trait and
not carried around everywhere.

Best,
Gary

Re: [GIT PULL PATCH 0/9] Rust changes for v7.4-rc1

[Andreas Hindborg]

"Gary Guo" <gary@garyguo.net> writes:

> On Wed Sep 30, 2026 at 4:06 PM BST, Thorsten Leemhuis wrote:
>> On 9/29/26 13:47, Jens Axboe wrote:
>>> On Tue, 29 Sep 2026 11:33:58 +0200, Andreas Hindborg wrote:
>>>> I have a number of Rust block layer patches I would ask you to pick for
>>>> v7.4. I have collected them into a patch series as well as a pull request
>>>> so you can use whatever is easier.
>>>>
>>>> The changes cover
>>>>
>>>>  - Style and formatting changes.
>>>>  - Documentation fixes.
>>>>  - Fixes for missing trait bounds that can cause API unsoundness.
>>>>  - A change to set the owner of the file operations vtable in `GenDisk`.
>>>>  - Two bug fixes for the rnull driver.
>>>>
>>>> [...]
>>> 
>>> Applied, thanks!
>>>  [...]
>>
>> This series showed up in next today and broke the build for me on
>> various Fedora releases for aarch64 and x86_64; reverting this series
>> fixed that from a quick build test limited to drivers/block/rnull/
>>
>> The full error msg is quote long, find the top of it below. Full log:
>> https://download.copr.fedorainfracloud.org/results/@kernel-vanilla/next/fedora-rawhide-aarch64/11055137-next-next-all/builder-live.log.gz
>
> The `Child: Send` bound is introduced in configfs:
> https://lore.kernel.org/all/tencent_05937A22D2DA2BAE808EF19E491AA109BC09@qq.com/.
> So this is more or less a semantic conflict.

I did not consider the interactions of the two trees together. Good
thing we have linux-next.

> However, the fundamental issue is that TagSet never implements Send/Sync, which
> means that "rust: block: fix `Send` bound for `GenDisk`" will unconditionally
> strip away the Send implementation, which is problematic.
>
> Something like this should fix the issue:
>
>     unsafe impl<T: Operations<QueueData: Send>> Send for TagSet<T> {}
>     unsafe impl<T: Operations<QueueData: Send>> Sync for TagSet<T> {}
>
> That said, I am not sure why the GenDisk need to carry `Arc<TagSet<T>>: Send`
> bound in the first place. Removing it should also fix the issue.

`GenDisk<T>` has a field of type `Arc<TagSet<T>>`, so for `GenDisk` to be
send, so must `Arc<TagSet<T>>`. That `Arc` may be dropped with the
`GenDisk` if it is the last reference.

> Also, the `QueueData: Send` bound should be part of the `Operations` trait and
> not carried around everywhere.

`QueueData` is not involved here. An unconditional implementation is
fine. I submitted a patch here [1], hopefully Jens can pick it soon so
next can be unbroken tomorrow.

Best regards,
Andreas Hindborg

[1] https://lore.kernel.org/r/20260930-tag-set-send-sync-v1-1-51acdb36f4bb@kernel.org