Re: [PATCH] rust: devres: ensure revocation is complete before device finishes unbinding

[Alice Ryhl <aliceryhl@google.com>]

On Sun, Jun 28, 2026 at 10:02:53PM +0200, Danilo Krummrich wrote:
> Now that the revocation Completion is in place, also address the
> symmetric case. When Devres::drop() wins the is_available swap and the
> devres callback loses, the callback returns to devres_release_all()
> without waiting. This means device unbinding can complete while
> Devres::drop() is still executing drop_in_place() on another CPU, which
> is a problem if T's destructor accesses device state.
> 
> Make the synchronization bidirectional. Whichever side performs
> drop_in_place() signals the Completion, and the other side waits.
> 
> This does not reintroduce the nested Devres deadlock fixed by commit
> ba268514ea14 ("rust: devres: fix race condition due to nesting"),
> because that deadlock was caused by drop waiting for the release
> callback to return (the old 'devm' Completion). Here, both sides only
> wait for drop_in_place() to finish, which completes within the current
> call chain. The Arc<Inner<T>> keeps the Inner allocation alive
> independently.
> 
> Cc: stable@vger.kernel.org
> Fixes: ba268514ea14 ("rust: devres: fix race condition due to nesting")
> Signed-off-by: Danilo Krummrich <dakr@kernel.org>

Reviewed-by: Alice Ryhl <aliceryhl@google.com>