[PATCH rust-next] rust: binder: refactor context management to use KVVec

[jkhall81 <jason.kei.hall@gmail.com>]

Replace the intrusive linked list management in context.rs with KVVec.
This modernization simplifies the ownership model by using standard
Arc-based tracking and moves away from manual unsafe list removals.

The refactor improves memory safety by leveraging Rust's contiguous
collection types while maintaining proper error propagation for
allocation failures during process registration.

Suggested-by: Alice Ryhl <aliceryhl@google.com>
Link: https://github.com/rust-for-linux/linux/issues/1215
Signed-off-by: jkhall81 <jason.kei.hall@gmail.com>
---
 drivers/android/binder/context.rs | 73 ++++++++++++++-----------------
 drivers/android/binder/process.rs |  4 +-
 2 files changed, 36 insertions(+), 41 deletions(-)

diff --git a/drivers/android/binder/context.rs b/drivers/android/binder/context.rs
index 3d135ec03ca7..83fa8a16662b 100644
--- a/drivers/android/binder/context.rs
+++ b/drivers/android/binder/context.rs
@@ -3,8 +3,8 @@
 // Copyright (C) 2025 Google LLC.
 
 use kernel::{
-    error::Error,
-    list::{List, ListArc, ListLinks},
+    alloc::kvec::{KVVec, KVec},
+    error::code::*,
     prelude::*,
     security,
     str::{CStr, CString},
@@ -17,22 +17,19 @@
 kernel::sync::global_lock! {
     // SAFETY: We call `init` in the module initializer, so it's initialized before first use.
     pub(crate) unsafe(uninit) static CONTEXTS: Mutex<ContextList> = ContextList {
-        list: List::new(),
+        contexts: KVVec::new(),
     };
 }
 
 pub(crate) struct ContextList {
-    list: List<Context>,
+    contexts: KVVec<Arc<Context>>,
 }
 
 pub(crate) fn get_all_contexts() -> Result<KVec<Arc<Context>>> {
     let lock = CONTEXTS.lock();
-
-    let count = lock.list.iter().count();
-
-    let mut ctxs = KVec::with_capacity(count, GFP_KERNEL)?;
-    for ctx in &lock.list {
-        ctxs.push(Arc::from(ctx), GFP_KERNEL)?;
+    let mut ctxs = KVec::with_capacity(lock.contexts.len(), GFP_KERNEL)?;
+    for ctx in lock.contexts.iter() {
+        ctxs.push(ctx.clone(), GFP_KERNEL)?;
     }
     Ok(ctxs)
 }
@@ -42,7 +39,7 @@ pub(crate) fn get_all_contexts() -> Result<KVec<Arc<Context>>> {
 struct Manager {
     node: Option<NodeRef>,
     uid: Option<Kuid>,
-    all_procs: List<Process>,
+    all_procs: KVVec<Arc<Process>>,
 }
 
 /// There is one context per binder file (/dev/binder, /dev/hwbinder, etc)
@@ -51,28 +48,16 @@ pub(crate) struct Context {
     #[pin]
     manager: Mutex<Manager>,
     pub(crate) name: CString,
-    #[pin]
-    links: ListLinks,
-}
-
-kernel::list::impl_list_arc_safe! {
-    impl ListArcSafe<0> for Context { untracked; }
-}
-kernel::list::impl_list_item! {
-    impl ListItem<0> for Context {
-        using ListLinks { self.links };
-    }
 }
 
 impl Context {
     pub(crate) fn new(name: &CStr) -> Result<Arc<Self>> {
         let name = CString::try_from(name)?;
-        let list_ctx = ListArc::pin_init::<Error>(
+        let ctx = Arc::pin_init(
             try_pin_init!(Context {
                 name,
-                links <- ListLinks::new(),
                 manager <- kernel::new_mutex!(Manager {
-                    all_procs: List::new(),
+                    all_procs: KVVec::new(),
                     node: None,
                     uid: None,
                 }, "Context::manager"),
@@ -80,8 +65,7 @@ pub(crate) fn new(name: &CStr) -> Result<Arc<Self>> {
             GFP_KERNEL,
         )?;
 
-        let ctx = list_ctx.clone_arc();
-        CONTEXTS.lock().list.push_back(list_ctx);
+        CONTEXTS.lock().contexts.push(ctx.clone(), GFP_KERNEL)?;
 
         Ok(ctx)
     }
@@ -90,17 +74,24 @@ pub(crate) fn new(name: &CStr) -> Result<Arc<Self>> {
     ///
     /// No-op if called twice.
     pub(crate) fn deregister(&self) {
-        // SAFETY: We never add the context to any other linked list than this one, so it is either
-        // in this list, or not in any list.
-        unsafe { CONTEXTS.lock().list.remove(self) };
+        // Safe removal using retain
+        CONTEXTS.lock().contexts.retain(|c| {
+            let p1 = Arc::as_ptr(c);
+            let p2 = self as *const Context;
+            p1 != p2
+        });
     }
 
-    pub(crate) fn register_process(self: &Arc<Self>, proc: ListArc<Process>) {
+    pub(crate) fn register_process(self: &Arc<Self>, proc: Arc<Process>) -> Result {
         if !Arc::ptr_eq(self, &proc.ctx) {
             pr_err!("Context::register_process called on the wrong context.");
-            return;
+            return Err(EINVAL);
         }
-        self.manager.lock().all_procs.push_back(proc);
+        self.manager
+            .lock()
+            .all_procs
+            .push(proc, GFP_KERNEL)
+            .map_err(Error::from)
     }
 
     pub(crate) fn deregister_process(self: &Arc<Self>, proc: &Process) {
@@ -108,8 +99,12 @@ pub(crate) fn deregister_process(self: &Arc<Self>, proc: &Process) {
             pr_err!("Context::deregister_process called on the wrong context.");
             return;
         }
-        // SAFETY: We just checked that this is the right list.
-        unsafe { self.manager.lock().all_procs.remove(proc) };
+        // Safe removal using retain
+        self.manager.lock().all_procs.retain(|p| {
+            let p1 = Arc::as_ptr(p);
+            let p2 = proc as *const Process;
+            p1 != p2
+        });
     }
 
     pub(crate) fn set_manager_node(&self, node_ref: NodeRef) -> Result {
@@ -160,11 +155,9 @@ pub(crate) fn for_each_proc<F>(&self, mut func: F)
 
     pub(crate) fn get_all_procs(&self) -> Result<KVec<Arc<Process>>> {
         let lock = self.manager.lock();
-        let count = lock.all_procs.iter().count();
-
-        let mut procs = KVec::with_capacity(count, GFP_KERNEL)?;
-        for proc in &lock.all_procs {
-            procs.push(Arc::from(proc), GFP_KERNEL)?;
+        let mut procs = KVec::with_capacity(lock.all_procs.len(), GFP_KERNEL)?;
+        for proc in lock.all_procs.iter() {
+            procs.push(Arc::clone(proc), GFP_KERNEL)?;
         }
         Ok(procs)
     }
diff --git a/drivers/android/binder/process.rs b/drivers/android/binder/process.rs
index 132055b4790f..c3676fc7785d 100644
--- a/drivers/android/binder/process.rs
+++ b/drivers/android/binder/process.rs
@@ -513,7 +513,9 @@ fn new(ctx: Arc<Context>, cred: ARef<Credential>) -> Result<Arc<Self>> {
         )?;
 
         let process = list_process.clone_arc();
-        process.ctx.register_process(list_process);
+        process
+            .ctx
+            .register_process(Arc::from(list_process.as_arc_borrow()))?;
 
         Ok(process)
     }
-- 
2.43.0