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android: binder: Don't get mm from task

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Use binder_alloc struct's mm_struct rather than getting
a reference to the mm struct through get_task_mm to
avoid a potential deadlock between lru lock, task lock and
dentry lock, since a thread can be holding the task lock
and the dentry lock while trying to acquire the lru lock.

Acked-by: Arve Hjønnevåg <arve@android.com>
Signed-off-by: Sherry Yang <sherryy@android.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Sherry Yang 2017-10-20 20:58:58 -04:00 committed by Greg Kroah-Hartman
parent 9d35593b4f
commit a0c2baaf81
2 changed files with 9 additions and 14 deletions
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22
drivers/android/binder_alloc.c
View File

@ -215,17 +215,12 @@ static int binder_update_page_range(struct binder_alloc *alloc, int allocate,
} }
} }
if (!vma && need_mm) if (!vma && need_mm && mmget_not_zero(alloc->vma_vm_mm))
mm = get_task_mm(alloc->tsk); mm = alloc->vma_vm_mm;
if (mm) { if (mm) {
down_write(&mm->mmap_sem); down_write(&mm->mmap_sem);
vma = alloc->vma; vma = alloc->vma;
if (vma && mm != alloc->vma_vm_mm) {
pr_err("%d: vma mm and task mm mismatch\n",
alloc->pid);
vma = NULL;
}
} }
if (!vma && need_mm) { if (!vma && need_mm) {
@ -720,6 +715,7 @@ int binder_alloc_mmap_handler(struct binder_alloc *alloc,
barrier(); barrier();
alloc->vma = vma; alloc->vma = vma;
alloc->vma_vm_mm = vma->vm_mm; alloc->vma_vm_mm = vma->vm_mm;
mmgrab(alloc->vma_vm_mm);
return 0; return 0;
@ -795,6 +791,8 @@ void binder_alloc_deferred_release(struct binder_alloc *alloc)
vfree(alloc->buffer); vfree(alloc->buffer);
} }
mutex_unlock(&alloc->mutex); mutex_unlock(&alloc->mutex);
if (alloc->vma_vm_mm)
mmdrop(alloc->vma_vm_mm);
binder_alloc_debug(BINDER_DEBUG_OPEN_CLOSE, binder_alloc_debug(BINDER_DEBUG_OPEN_CLOSE,
"%s: %d buffers %d, pages %d\n", "%s: %d buffers %d, pages %d\n",
@ -889,7 +887,6 @@ int binder_alloc_get_allocated_count(struct binder_alloc *alloc)
void binder_alloc_vma_close(struct binder_alloc *alloc) void binder_alloc_vma_close(struct binder_alloc *alloc)
{ {
WRITE_ONCE(alloc->vma, NULL); WRITE_ONCE(alloc->vma, NULL);
WRITE_ONCE(alloc->vma_vm_mm, NULL);
} }
/** /**
@ -926,9 +923,9 @@ enum lru_status binder_alloc_free_page(struct list_head *item,
page_addr = (uintptr_t)alloc->buffer + index * PAGE_SIZE; page_addr = (uintptr_t)alloc->buffer + index * PAGE_SIZE;
vma = alloc->vma; vma = alloc->vma;
if (vma) { if (vma) {
mm = get_task_mm(alloc->tsk); if (!mmget_not_zero(alloc->vma_vm_mm))
if (!mm) goto err_mmget;
goto err_get_task_mm_failed; mm = alloc->vma_vm_mm;
if (!down_write_trylock(&mm->mmap_sem)) if (!down_write_trylock(&mm->mmap_sem))
goto err_down_write_mmap_sem_failed; goto err_down_write_mmap_sem_failed;
} }
@ -963,7 +960,7 @@ enum lru_status binder_alloc_free_page(struct list_head *item,
err_down_write_mmap_sem_failed: err_down_write_mmap_sem_failed:
mmput_async(mm); mmput_async(mm);
err_get_task_mm_failed: err_mmget:
err_page_already_freed: err_page_already_freed:
mutex_unlock(&alloc->mutex); mutex_unlock(&alloc->mutex);
err_get_alloc_mutex_failed: err_get_alloc_mutex_failed:
@ -1002,7 +999,6 @@ struct shrinker binder_shrinker = {
*/ */
void binder_alloc_init(struct binder_alloc *alloc) void binder_alloc_init(struct binder_alloc *alloc)
{ {
alloc->tsk = current->group_leader;
alloc->pid = current->group_leader->pid; alloc->pid = current->group_leader->pid;
mutex_init(&alloc->mutex); mutex_init(&alloc->mutex);
INIT_LIST_HEAD(&alloc->buffers); INIT_LIST_HEAD(&alloc->buffers);

1
drivers/android/binder_alloc.h
View File

@ -100,7 +100,6 @@ struct binder_lru_page {
*/ */
struct binder_alloc { struct binder_alloc {
struct mutex mutex; struct mutex mutex;
struct task_struct *tsk;
struct vm_area_struct *vma; struct vm_area_struct *vma;
struct mm_struct *vma_vm_mm; struct mm_struct *vma_vm_mm;
void *buffer; void *buffer;