binder: Store lru freelist in binder_alloc

Store a pointer to the free pages list that the binder allocator should
use for a process inside of struct binder_alloc. This change allows
binder allocator code to be tested and debugged deterministically while
a system is using binder; i.e., without interfering with other binder
processes and independently of the shrinker. This is necessary to
convert the current binder_alloc_selftest into a kunit test that does
not rely on hijacking an existing binder_proc to run.

A binder process's binder_alloc->freelist should not be changed after
it is initialized. A sole exception is the process that runs the
existing binder_alloc selftest. Its freelist can be temporarily replaced
for the duration of the test because it runs as a single thread before
any pages can be added to the global binder freelist, and the test frees
every page it allocates before dropping the binder_selftest_lock. This
exception allows the existing selftest to be used to check for
regressions, but it will be dropped when the binder_alloc tests are
converted to kunit in a subsequent patch in this series.

Signed-off-by: Tiffany Yang <ynaffit@google.com>
Acked-by: Carlos Llamas <cmllamas@google.com>
Link: https://lore.kernel.org/r/20250714185321.2417234-3-ynaffit@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 16 insertions, 9 deletions

diff --git a/drivers/android/binder_alloc.c b/drivers/android/binder_alloc.c
index a0a7cb58fc05..0476e8c2b0fb 100644
--- a/drivers/android/binder_alloc.c
+++ b/drivers/android/binder_alloc.c
@@ -26,7 +26,7 @@
 #include "binder_alloc.h"
 #include "binder_trace.h"
 
-struct list_lru binder_freelist;
+static struct list_lru binder_freelist;
 
 static DEFINE_MUTEX(binder_alloc_mmap_lock);
 
@@ -206,7 +206,7 @@ static void binder_lru_freelist_add(struct binder_alloc *alloc,
 
 		trace_binder_free_lru_start(alloc, index);
 
-		ret = list_lru_add(&binder_freelist,
+		ret = list_lru_add(alloc->freelist,
 				   page_to_lru(page),
 				   page_to_nid(page),
 				   NULL);
@@ -405,7 +405,7 @@ static void binder_lru_freelist_del(struct binder_alloc *alloc,
 		if (page) {
 			trace_binder_alloc_lru_start(alloc, index);
 
-			on_lru = list_lru_del(&binder_freelist,
+			on_lru = list_lru_del(alloc->freelist,
 					      page_to_lru(page),
 					      page_to_nid(page),
 					      NULL);
@@ -1003,7 +1003,7 @@ void binder_alloc_deferred_release(struct binder_alloc *alloc)
 			if (!page)
 				continue;
 
-			on_lru = list_lru_del(&binder_freelist,
+			on_lru = list_lru_del(alloc->freelist,
 					      page_to_lru(page),
 					      page_to_nid(page),
 					      NULL);
@@ -1223,6 +1223,17 @@ binder_shrink_scan(struct shrinker *shrink, struct shrink_control *sc)
 
 static struct shrinker *binder_shrinker;
 
+static void __binder_alloc_init(struct binder_alloc *alloc,
+				struct list_lru *freelist)
+{
+	alloc->pid = current->group_leader->pid;
+	alloc->mm = current->mm;
+	mmgrab(alloc->mm);
+	mutex_init(&alloc->mutex);
+	INIT_LIST_HEAD(&alloc->buffers);
+	alloc->freelist = freelist;
+}
+
 /**
  * binder_alloc_init() - called by binder_open() for per-proc initialization
  * @alloc: binder_alloc for this proc
@@ -1232,11 +1243,7 @@ static struct shrinker *binder_shrinker;
  */
 void binder_alloc_init(struct binder_alloc *alloc)
 {
-	alloc->pid = current->group_leader->pid;
-	alloc->mm = current->mm;
-	mmgrab(alloc->mm);
-	mutex_init(&alloc->mutex);
-	INIT_LIST_HEAD(&alloc->buffers);
+	__binder_alloc_init(alloc, &binder_freelist);
 }
 
 int binder_alloc_shrinker_init(void)