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 <[e-mail]>
Reviewed-by: Christian König <[e-mail]>
Signed-off-by: Daniel Vetter <[e-mail]>
Cc: Sumit Semwal <[e-mail]>
Cc: "Christian König" <[e-mail]>
Cc: [e-mail]
Cc: [e-mail]
Cc: Dave Chinner <[e-mail]>
Cc: Qian Cai <[e-mail]>
Cc: [e-mail]
Cc: [e-mail]
Cc: Thomas Hellström (Intel) <[e-mail]>
Cc: Andrew Morton <[e-mail]>
Cc: Jason Gunthorpe <[e-mail]>
Cc: [e-mail]
Cc: [e-mail]
Cc: Maarten Lankhorst <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

drivers/dma-buf/dma-resv.c

···
 	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);
···
 	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();