From: Carlos Llamas cmllamas@google.com
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@oracle.com Cc: Suren Baghdasaryan surenb@google.com Cc: stable@vger.kernel.org Signed-off-by: Carlos Llamas cmllamas@google.com Link: https://lore.kernel.org/r/20230502201220.1756319-3-cmllamas@google.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org [cmllamas: fixed minor merge conflict in binder_alloc_set_vma()] Signed-off-by: Carlos Llamas cmllamas@google.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- 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;