[PATCH] rust: block: require `Sync` for `Operations::QueueData`

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

The queue data installed in a `GenDisk` is stored in the request queue and
handed back to the driver as a shared borrow through the `queue_rq` and
`commit_rqs` callbacks. Both callbacks obtain that borrow via
`ForeignOwnable::borrow` and may execute concurrently on several CPUs,
since the block layer runs one hardware queue per CPU. That means a shared
reference to the same queue data can be live on multiple threads at once,
which is only sound when the referent is `Sync`.

The initial `GenDisk` private data support omitted this bound, so a
driver could install a non-`Sync` type as queue data and then access
it concurrently from multiple CPUs without synchronization. Add a
`Sync` bound to the `QueueData` associated type to rule that out.

Fixes: 90d952fac8ac ("rust: block: add `GenDisk` private data support")
Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>
---
 rust/kernel/block/mq/operations.rs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/rust/kernel/block/mq/operations.rs b/rust/kernel/block/mq/operations.rs
index 8ad46129a52c..89029f468f44 100644
--- a/rust/kernel/block/mq/operations.rs
+++ b/rust/kernel/block/mq/operations.rs
@@ -30,7 +30,7 @@
 pub trait Operations: Sized {
     /// Data associated with the `struct request_queue` that is allocated for
     /// the `GenDisk` associated with this `Operations` implementation.
-    type QueueData: ForeignOwnable;
+    type QueueData: ForeignOwnable + Sync;
 
     /// Called by the kernel to queue a request with the driver. If `is_last` is
     /// `false`, the driver is allowed to defer committing the request.

---
base-commit: 7fd2df204f342fc17d1a0bfcd474b24232fb0f32
change-id: 20260608-queue-data-sync-80b66ab312ac

Best regards,
--  
Andreas Hindborg <a.hindborg@kernel.org>