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binder: add lockless binder_alloc_(set|get)_vma()

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commit 0fa53349c3 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: a43cfc87ca ("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>
This commit is contained in:
Carlos Llamas 2023-05-30 19:43:37 +00:00 committed by Greg Kroah-Hartman
parent dd7aff43d0
commit 1cae0d5136
1 changed files with 7 additions and 15 deletions
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22
drivers/android/binder_alloc.c
View file

@ -309,29 +309,18 @@ static int binder_update_page_range(struct binder_alloc *alloc, int allocate,
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_alloc_new_buf_locked(
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 binder_alloc *alloc,
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;