ANDROID: ashmem_rust: move shrinker to its own global

To support changing whether the shrinker is registered at runtime, move
it to a new global variable that will keep track of the current state.
The actual support for changing the state at runtime happens in a later
commit.

Bug: 370906207
Change-Id: Ic635c2cdfbe466f9a03583de881cbf63e39957df
Signed-off-by: Alice Ryhl <aliceryhl@google.com>

drivers/staging/android/ashmem_range.rs

@@ -5,8 +5,12 @@
 //! Keeps track of unpinned ranges in an ashmem file.
 
 use crate::{
-    ashmem_shrinker::{CountObjects, ScanObjects, ShrinkControl, Shrinker},
+    ashmem_shrinker::{
+        self, CountObjects, ScanObjects, ShrinkControl, Shrinker, ShrinkerBuilder,
+        ShrinkerRegistration,
+    },
     shmem::ShmemFile,
+    AshmemModule,
 };
 use core::{
     mem::MaybeUninit,
@@ -14,6 +18,8 @@ use core::{
     sync::atomic::{AtomicUsize, Ordering},
 };
 use kernel::{
+    alloc::AllocError,
+    c_str,
     list::{List, ListArc, ListLinks},
     page::PAGE_SIZE,
     prelude::*,
@@ -440,6 +446,26 @@ impl Shrinker for super::AshmemModule {
     }
 }
 
+/// Make line below shorter.
+type AshmemShrinkerType = Option<ShrinkerRegistration<AshmemModule>>;
+
+kernel::sync::global_lock! {
+    // SAFETY: We call `init` as the very first thing in the initialization of this module, so
+    // there are no calls to `lock` before `init` is called.
+    pub(crate) unsafe(uninit) static ASHMEM_SHRINKER: Mutex<AshmemShrinkerType> = None;
+}
+
+pub(crate) fn register_shrinker() -> Result<(), AllocError> {
+    let mut lock = ASHMEM_SHRINKER.lock();
+    if lock.is_none() {
+        let mut shrinker = ShrinkerBuilder::new(c_str!("android-ashmem"))?;
+        shrinker.set_seeks(4 * ashmem_shrinker::DEFAULT_SEEKS);
+
+        *lock = Some(shrinker.register(()));
+    }
+    Ok(())
+}
+
 #[cfg(test)]
 fn range_test() -> Result {
     fn get_random(max: usize) -> usize {

drivers/staging/android/ashmem_rust.rs

@@ -42,7 +42,6 @@ const PROT_WRITE: usize = bindings::PROT_WRITE as usize;
 const PROT_MASK: usize = PROT_EXEC | PROT_READ | PROT_WRITE;
 
 mod ashmem_shrinker;
-use ashmem_shrinker::{ShrinkerBuilder, ShrinkerRegistration};
 
 mod ashmem_range;
 use ashmem_range::{Area, AshmemGuard, NewRange, ASHMEM_MUTEX, LRU_COUNT};
@@ -79,7 +78,6 @@ module! {
 
 struct AshmemModule {
     _misc: Pin<Box<MiscDeviceRegistration<Ashmem>>>,
-    _shrinker: ShrinkerRegistration<Self>,
 }
 
 impl kernel::Module for AshmemModule {
@@ -88,11 +86,12 @@ impl kernel::Module for AshmemModule {
         unsafe { shmem::SHMEM_FOPS_ONCE.init() };
         // SAFETY: Called once since this is the module initializer.
         unsafe { ASHMEM_MUTEX.init() };
+        // SAFETY: Called once since this is the module initializer.
+        unsafe { ashmem_range::ASHMEM_SHRINKER.init() };
 
         pr_info!("Using Rust implementation.");
 
-        let mut shrinker = ShrinkerBuilder::new(c_str!("android-ashmem"))?;
-        shrinker.set_seeks(4 * ashmem_shrinker::DEFAULT_SEEKS);
+        ashmem_range::register_shrinker()?;
 
         Ok(Self {
             _misc: Box::pin_init(
@@ -101,7 +100,6 @@ impl kernel::Module for AshmemModule {
                 }),
                 GFP_KERNEL,
             )?,
-            _shrinker: shrinker.register(()),
         })
     }
 }