Re: [PATCH] rust: devres: fix race between concurrent revokers

[Alice Ryhl]

On Sun, Jun 28, 2026 at 07:44:38PM +0200, Danilo Krummrich wrote:
> There is a potential race condition when two paths try to revoke a
> Devres concurrently.
> 
> The driver core's devres_release_all() calls Revocable::revoke() via the
> release callback, while Devres::drop() calls revoke_nosync() on another
> CPU.
> 
> The revoker that does not claim the is_available swap returns
> immediately, but the revoker that did may still be executing
> drop_in_place() on the inner data. This can cause a use-after-free when
> the other revoker's caller proceeds to drop adjacent resources that
> drop_in_place() still references (e.g., Devres<DmaMappedSgt> racing with
> SGTable freeing the backing sg_table and pages).
> 
> Fix this by adding a Completion. The release callback signals the
> Completion after revoke() finishes, and Devres::drop() waits for it when
> it loses the is_available swap. This ensures the wrapped object is fully
> torn down before Devres::drop() returns.
> 
> Cc: stable@xxxxxxxxxxxxxxx
> Reported-by: Sashiko <sashiko-bot@xxxxxxxxxx>
> Closes: https://lore.kernel.org/dri-devel/20260612202841.2577C1F000E9@xxxxxxxxxxxxxxx/
> Fixes: 05aa6fb1c21d ("rust: scatterlist: Add abstraction for sg_table")
> Signed-off-by: Danilo Krummrich <dakr@xxxxxxxxxx>

Reviewed-by: Alice Ryhl <aliceryhl@xxxxxxxxxx>