[PATCH v2 4/5] binder: Remove mmap_lock fallback

[Dave Hansen]

From: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>

Previously, the per-VMA locking could fail in the face of writers
which necessitate a fallback to mmap_lock. The new
vma_start_read_unlocked() will wait for writers instead of failing.

Use the new helper. Wait for writers. Remove the fallback to mmap_lock.

Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Acked-by: Lorenzo Stoakes <ljs@xxxxxxxxxx>
Reviewed-by: Suren Baghdasaryan <surenb@xxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: "Liam R. Howlett" <Liam.Howlett@xxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxxxxx>
Cc: Shakeel Butt <shakeel.butt@xxxxxxxxx>
Cc: linux-mm@xxxxxxxxx
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Cc: Arve Hjønnevåg <arve@xxxxxxxxxxx>
Cc: Todd Kjos <tkjos@xxxxxxxxxxx>
Cc: Christian Brauner <christian@xxxxxxxxxx>
Cc: Carlos Llamas <cmllamas@xxxxxxxxxx>
Cc: Alice Ryhl <aliceryhl@xxxxxxxxxx>
Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
Cc: David Ahern <dsahern@xxxxxxxxxx>
Cc: netdev@xxxxxxxxxxxxxxx

---

 b/drivers/android/binder_alloc.c |   17 +++++------------
 1 file changed, 5 insertions(+), 12 deletions(-)

diff -puN drivers/android/binder_alloc.c~binder-vma-waiter drivers/android/binder_alloc.c
--- a/drivers/android/binder_alloc.c~binder-vma-waiter	2026-06-10 15:57:56.419452721 -0700
+++ b/drivers/android/binder_alloc.c	2026-06-10 15:57:56.423452863 -0700
@@ -259,21 +259,14 @@ static int binder_page_insert(struct bin
 	struct vm_area_struct *vma;
 	int ret = -ESRCH;
 
-	/* attempt per-vma lock first */
-	vma = lock_vma_under_rcu(mm, addr);
-	if (vma) {
-		if (binder_alloc_is_mapped(alloc))
-			ret = vm_insert_page(vma, addr, page);
-		vma_end_read(vma);
+	vma = vma_start_read_unlocked(mm, addr);
+	if (!vma)
 		return ret;
-	}
 
-	/* fall back to mmap_lock */
-	mmap_read_lock(mm);
-	vma = vma_lookup(mm, addr);
-	if (vma && binder_alloc_is_mapped(alloc))
+	if (binder_alloc_is_mapped(alloc))
 		ret = vm_insert_page(vma, addr, page);
-	mmap_read_unlock(mm);
+
+	vma_end_read(vma);
 
 	return ret;
 }
_