From: Carlos Llamas <cmllamas@xxxxxxxxxx>
commit 0fa53349c3acba0239369ba4cd133740a408d246 upstream.
Bring back the original lockless design in binder_alloc to determine
whether the buffer setup has been completed by the ->mmap() handler.
However, this time use smp_load_acquire() and smp_store_release() to
wrap all the ordering in a single macro call.
Also, add comments to make it evident that binder uses alloc->vma to
determine when the binder_alloc has been fully initialized. In these
scenarios acquiring the mmap_lock is not required.
Fixes: a43cfc87caaf ("android: binder: stop saving a pointer to the VMA")
Cc: Liam Howlett <liam.howlett@xxxxxxxxxx>
Cc: Suren Baghdasaryan <surenb@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Carlos Llamas <cmllamas@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20230502201220.1756319-3-cmllamas@xxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
[cmllamas: fixed minor merge conflict in binder_alloc_set_vma()]
Signed-off-by: Carlos Llamas <cmllamas@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/android/binder_alloc.c | 22 +++++++---------------
1 file changed, 7 insertions(+), 15 deletions(-)
--- a/drivers/android/binder_alloc.c
+++ b/drivers/android/binder_alloc.c
@@ -309,29 +309,18 @@ err_no_vma:
return vma ? -ENOMEM : -ESRCH;
}
-
static inline void binder_alloc_set_vma(struct binder_alloc *alloc,
struct vm_area_struct *vma)
{
- /*
- * If we see alloc->vma is not NULL, buffer data structures set up
- * completely. Look at smp_rmb side binder_alloc_get_vma.
- */
- smp_wmb();
- alloc->vma = vma;
+ /* pairs with smp_load_acquire in binder_alloc_get_vma() */
+ smp_store_release(&alloc->vma, vma);
}
static inline struct vm_area_struct *binder_alloc_get_vma(
struct binder_alloc *alloc)
{
- struct vm_area_struct *vma = NULL;
-
- if (alloc->vma) {
- /* Look at description in binder_alloc_set_vma */
- smp_rmb();
- vma = alloc->vma;
- }
- return vma;
+ /* pairs with smp_store_release in binder_alloc_set_vma() */
+ return smp_load_acquire(&alloc->vma);
}
static bool debug_low_async_space_locked(struct binder_alloc *alloc, int pid)
@@ -394,6 +383,7 @@ static struct binder_buffer *binder_allo
size_t size, data_offsets_size;
int ret;
+ /* Check binder_alloc is fully initialized */
if (!binder_alloc_get_vma(alloc)) {
binder_alloc_debug(BINDER_DEBUG_USER_ERROR,
"%d: binder_alloc_buf, no vma\n",
@@ -789,6 +779,8 @@ int binder_alloc_mmap_handler(struct bin
buffer->free = 1;
binder_insert_free_buffer(alloc, buffer);
alloc->free_async_space = alloc->buffer_size / 2;
+
+ /* Signal binder_alloc is fully initialized */
binder_alloc_set_vma(alloc, vma);
return 0;
