rust_binder: Implement BINDER_DEBUG_DEATH_NOTIFICATION

This adds dynamic debug logs for:
- Memory allocation (OOM) failures when requesting
  death notifications
- Registration and cancellation lifecycle events
  (BC_REQUEST / BC_CLEAR)
- Delivery of death notification events to userspace
  (BR_DEAD_BINDER)

Reviewed-by: Carlos Llamas <cmllamas@google.com>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Signed-off-by: Jahnavi MN <jahnavimn@google.com>
Link: https://patch.msgid.link/20260716-rust_binder_debug_mask-v4-6-3d7436c2d2f2@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/android/binder/node.rs

@@ -1107,6 +1107,11 @@ fn do_work(
             // We're still holding the inner lock, so it cannot be aborted while we insert it into
             // the delivered list.
             process_inner.death_delivered(self.clone());
+            binder_debug!(
+                DeathNotification,
+                "sending death notification, cookie {:016x}",
+                cookie
+            );
             BR_DEAD_BINDER
         };
 

drivers/android/binder/process.rs

@@ -1253,6 +1253,10 @@ pub(crate) fn request_death(
         // Queue BR_ERROR if we can't allocate memory for the death notification.
         let death = UniqueArc::new_uninit(GFP_KERNEL).inspect_err(|_| {
             thread.push_return_work(BR_ERROR);
+            binder_debug!(
+                DeathNotification,
+                "BC_REQUEST_DEATH_NOTIFICATION failed due to memory allocation failure"
+            );
         })?;
         let mut refs = self.node_refs.lock();
         let Some(info) = refs.by_handle.get_mut(&handle) else {
@@ -1296,6 +1300,11 @@ pub(crate) fn request_death(
                 info.node_ref().node.add_death(death, &mut owner_inner);
             }
         }
+        binder_debug!(
+            DeathNotification,
+            "BC_REQUEST_DEATH_NOTIFICATION handle {handle} cookie {:016x}",
+            cookie
+        );
         Ok(())
     }
 
@@ -1339,6 +1348,11 @@ pub(crate) fn clear_death(&self, reader: &mut UserSliceReader, thread: &Thread)
             }
         }
 
+        binder_debug!(
+            DeathNotification,
+            "BC_CLEAR_DEATH_NOTIFICATION handle {handle} cookie {:016x}",
+            cookie
+        );
         Ok(())
     }