Re: [PATCH] rust: configfs: skip unregister after failed registration

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

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

> On Tue Aug 18, 2026 at 9:11 AM BST, Younes Akhouayri via B4 Relay wrote:
>> From: Younes Akhouayri <git@younes.io>
>>
>> Subsystem::new() calls configfs_register_subsystem() from a fallible
>> pin_chain callback. If registration fails, ChainPinInit drops the
>> already initialized Subsystem. Its PinnedDrop currently calls
>> configfs_unregister_subsystem() unconditionally.
>>
>> configfs_unregister_subsystem() requires registration to have completed
>> and immediately dereferences the subsystem dentry. Registering a
>> duplicate subsystem name returns -EEXIST before installing that dentry,
>> so the cleanup path dereferences NULL and panics the kernel.
>>
>> Track successful registration explicitly and only unregister in that
>> state. Keep mutex destruction unconditional because it is initialized
>> before registration.
>>
>> Fixes: 446cafc295bf ("rust: configfs: introduce rust support for configfs")
>> Signed-off-by: Younes Akhouayri <git@younes.io>
>> ---
>>  rust/kernel/configfs.rs | 14 ++++++++++----
>>  1 file changed, 10 insertions(+), 4 deletions(-)
>>
>> diff --git a/rust/kernel/configfs.rs b/rust/kernel/configfs.rs
>> index cd082b83e9e7..f358e227ce09 100644
>> --- a/rust/kernel/configfs.rs
>> +++ b/rust/kernel/configfs.rs
>> @@ -130,6 +130,7 @@ pub struct Subsystem<Data> {
>>      subsystem: Opaque<bindings::configfs_subsystem>,
>>      #[pin]
>>      data: Data,
>> +    registered: bool,
>
> No flag just for destruction. Please change new logic to avoid needing this.

I guess we can have a local `UnregisteredSubsystem` that we can
cast to a `Subsystem` once registration succeeds. Is that what you have
in mind?


Best regards,
Andreas Hindborg