dma-resv: lockdep-prime address_space->i_mmap_rwsem for dma-resv

GPU drivers need this in their shrinkers, to be able to throw out
mmap'ed buffers. Note that we also need dma_resv_lock in shrinkers,
but that loop is resolved by trylocking in shrinkers.

So full hierarchy is now (ignore some of the other branches we already
have primed):

mmap_read_lock -> dma_resv -> shrinkers -> i_mmap_lock_write

I hope that's not inconsistent with anything mm or fs does, adding
relevant people.
Reviewed-by: Thomas Hellström <thomas.hellstrom@intel.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Cc: "Christian König" <christian.koenig@amd.com>
Cc: linux-media@vger.kernel.org
Cc: linaro-mm-sig@lists.linaro.org
Cc: Dave Chinner <david@fromorbit.com>
Cc: Qian Cai <cai@lca.pw>
Cc: linux-xfs@vger.kernel.org
Cc: linux-fsdevel@vger.kernel.org
Cc: Thomas Hellström (Intel) <thomas_os@shipmail.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Jason Gunthorpe <jgg@mellanox.com>
Cc: linux-mm@kvack.org
Cc: linux-rdma@vger.kernel.org
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200728135839.1035515-1-daniel.vetter@ffwll.ch

drivers/dma-buf/dma-resv.c

@@ -98,12 +98,14 @@ static int __init dma_resv_lockdep(void)
 	struct mm_struct *mm = mm_alloc();
 	struct ww_acquire_ctx ctx;
 	struct dma_resv obj;
+	struct address_space mapping;
 	int ret;
 
 	if (!mm)
 		return -ENOMEM;
 
 	dma_resv_init(&obj);
+	address_space_init_once(&mapping);
 
 	mmap_read_lock(mm);
 	ww_acquire_init(&ctx, &reservation_ww_class);
@@ -111,6 +113,9 @@ static int __init dma_resv_lockdep(void)
 	if (ret == -EDEADLK)
 		dma_resv_lock_slow(&obj, &ctx);
 	fs_reclaim_acquire(GFP_KERNEL);
+	/* for unmap_mapping_range on trylocked buffer objects in shrinkers */
+	i_mmap_lock_write(&mapping);
+	i_mmap_unlock_write(&mapping);
 #ifdef CONFIG_MMU_NOTIFIER
 	lock_map_acquire(&__mmu_notifier_invalidate_range_start_map);
 	__dma_fence_might_wait();