btrfs: replace kmap_atomic() with kmap_local_page()

kmap_atomic() is being deprecated in favor of kmap_local_page() where it
is feasible. With kmap_local_page() mappings are per thread, CPU local,
and not globally visible.

The last use of kmap_atomic is in inode.c where the context is atomic [1]
and can be safely replaced by kmap_local_page.

Tested with xfstests on a QEMU + KVM 32-bits VM with 4GB RAM and booting a
kernel with HIGHMEM64GB enabled.

[1] https://lore.kernel.org/linux-btrfs/20220601132545.GM20633@twin.jikos.cz/

Suggested-by: Ira Weiny <ira.weiny@intel.com>
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/inode.c

@@ -333,9 +333,9 @@ static int insert_inline_extent(struct btrfs_trans_handle *trans,
 			cur_size = min_t(unsigned long, compressed_size,
 				       PAGE_SIZE);
 
-			kaddr = kmap_atomic(cpage);
+			kaddr = kmap_local_page(cpage);
 			write_extent_buffer(leaf, kaddr, ptr, cur_size);
-			kunmap_atomic(kaddr);
+			kunmap_local(kaddr);
 
 			i++;
 			ptr += cur_size;
@@ -346,9 +346,9 @@ static int insert_inline_extent(struct btrfs_trans_handle *trans,
 	} else {
 		page = find_get_page(inode->vfs_inode.i_mapping, 0);
 		btrfs_set_file_extent_compression(leaf, ei, 0);
-		kaddr = kmap_atomic(page);
+		kaddr = kmap_local_page(page);
 		write_extent_buffer(leaf, kaddr, ptr, size);
-		kunmap_atomic(kaddr);
+		kunmap_local(kaddr);
 		put_page(page);
 	}
 	btrfs_mark_buffer_dirty(leaf);