btrfs: subpage: do more sanity checks on metadata page dirtying

For btree_set_page_dirty(), we should also check the extent buffer
sanity for subpage support.

Unlike the regular sector size case, since one page can contain multiple
extent buffers, we need to make sure there is at least one dirty extent
buffer in the page.

So this patch will iterate through the btrfs_subpage::dirty_bitmap
to get the extent buffers, and check if any dirty extent buffer in the page
range has EXTENT_BUFFER_DIRTY and proper refs.
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/disk-io.c

@@ -42,6 +42,7 @@
 #include "discard.h"
 #include "space-info.h"
 #include "zoned.h"
+#include "subpage.h"
 
 #define BTRFS_SUPER_FLAG_SUPP	(BTRFS_HEADER_FLAG_WRITTEN |\
 				 BTRFS_HEADER_FLAG_RELOC |\
@@ -992,14 +993,48 @@ static void btree_invalidatepage(struct page *page, unsigned int offset,
 static int btree_set_page_dirty(struct page *page)
 {
 #ifdef DEBUG
+	struct btrfs_fs_info *fs_info = btrfs_sb(page->mapping->host->i_sb);
+	struct btrfs_subpage *subpage;
 	struct extent_buffer *eb;
+	int cur_bit = 0;
+	u64 page_start = page_offset(page);
 
+	if (fs_info->sectorsize == PAGE_SIZE) {
 		BUG_ON(!PagePrivate(page));
 		eb = (struct extent_buffer *)page->private;
 		BUG_ON(!eb);
 		BUG_ON(!test_bit(EXTENT_BUFFER_DIRTY, &eb->bflags));
 		BUG_ON(!atomic_read(&eb->refs));
 		btrfs_assert_tree_locked(eb);
+		return __set_page_dirty_nobuffers(page);
+	}
+	ASSERT(PagePrivate(page) && page->private);
+	subpage = (struct btrfs_subpage *)page->private;
+
+	ASSERT(subpage->dirty_bitmap);
+	while (cur_bit < BTRFS_SUBPAGE_BITMAP_SIZE) {
+		unsigned long flags;
+		u64 cur;
+		u16 tmp = (1 << cur_bit);
+
+		spin_lock_irqsave(&subpage->lock, flags);
+		if (!(tmp & subpage->dirty_bitmap)) {
+			spin_unlock_irqrestore(&subpage->lock, flags);
+			cur_bit++;
+			continue;
+		}
+		spin_unlock_irqrestore(&subpage->lock, flags);
+		cur = page_start + cur_bit * fs_info->sectorsize;
+
+		eb = find_extent_buffer(fs_info, cur);
+		ASSERT(eb);
+		ASSERT(test_bit(EXTENT_BUFFER_DIRTY, &eb->bflags));
+		ASSERT(atomic_read(&eb->refs));
+		btrfs_assert_tree_locked(eb);
+		free_extent_buffer(eb);
+
+		cur_bit += (fs_info->nodesize >> fs_info->sectorsize_bits);
+	}
 #endif
 	return __set_page_dirty_nobuffers(page);
 }