btrfs: protect sb_write_pointer() with invalidate lock

sb_write_pointer() reads the super block from the block device page cache
using read_cache_page_gfp(). This has the same race with BLKBSZSET as the
one fixed by commit 3f29d66 ("btrfs: sync read disk super and set
block size").

Take the mapping invalidate lock around read_cache_page_gfp() to
serialize the read against block size changes.

Signed-off-by: KangNing Liao <lkangn.kernel@gmail.com>
Reviewed-by: Qu Wenruo <wqu@suse.com>

Author: KangNing Liao

fs/btrfs/zoned.c

@@ -131,8 +131,10 @@ static int sb_write_pointer(struct block_device *bdev, struct blk_zone *zones,
 			u64 bytenr = ALIGN_DOWN(zone_end, BTRFS_SUPER_INFO_SIZE) -
 						BTRFS_SUPER_INFO_SIZE;
 
+			filemap_invalidate_lock(mapping);
 			page[i] = read_cache_page_gfp(mapping,
 					bytenr >> PAGE_SHIFT, GFP_NOFS);
+			filemap_invalidate_unlock(mapping);
 			if (IS_ERR(page[i])) {
 				if (i == 1)
 					btrfs_release_disk_super(super[0]);