rust_binder: avoid dropping NodeRef in update_ref() under lock

In preparation for changing the node_refs lock to a spinlock, move the
cleanup of NodeRefInfo in update_ref() so that it occurs without the
node_refs lock held. This avoids dropping an Arc<Node> with the lock
held. Furthermore, the NodeDeath field is kept in the NodeRefInfo to be
dropped outside the lock as well.

The removal from the rbtree is updated to use remove_node(), which keeps
the rbtree node allocation until after node_refs is unlocked as well.
This is not strictly necessary as it just moves a kfree() outside the
lock, but there's no reason to invoke the kfree() under the lock if we
can easily avoid it, so avoid it.

Reviewed-by: Matthew Maurer <mmaurer@google.com>
Signed-off-by: Alice Ryhl <aliceryhl@google.com>
Link: https://patch.msgid.link/20260615-binder-noderefs-spin-v3-2-3235f5a3e0a0@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 8 insertions, 4 deletions

diff --git a/drivers/android/binder/process.rs b/drivers/android/binder/process.rs
index 99d1a7ade599..73a2582c4d9c 100644
--- a/drivers/android/binder/process.rs
+++ b/drivers/android/binder/process.rs
@@ -942,13 +942,17 @@ impl Process {
 
         // To preserve original binder behaviour, we only fail requests where the manager tries to
         // increment references on itself.
+        let _to_free_by_handle;
+        let _to_free_by_node;
         let mut refs = self.node_refs.lock();
         if let Some(info) = refs.by_handle.get_mut(&handle) {
             if info.node_ref().update(inc, strong) {
                 // Clean up death if there is one attached to this node reference.
-                if let Some(death) = info.death().take() {
+                //
+                // We remove the entire `info` below, so no need to remove `death` from `info`.
+                if let Some(death) = info.death().as_ref() {
                     death.set_cleared(true);
-                    self.remove_from_delivered_deaths(&death);
+                    self.remove_from_delivered_deaths(death);
                 }
 
                 // Remove reference from process tables, and from the node's `refs` list.
@@ -957,8 +961,8 @@ impl Process {
                 unsafe { info.node_ref2().node.remove_node_info(info) };
 
                 let id = info.node_ref().node.global_id();
-                refs.by_handle.remove(&handle);
-                refs.by_node.remove(&id);
+                _to_free_by_handle = refs.by_handle.remove_node(&handle);
+                _to_free_by_node = refs.by_node.remove_node(&id);
                 refs.handle_is_present.release_id(handle as usize);
 
                 if let Some(shrink) = refs.handle_is_present.shrink_request() {