md-bitmap: don't use ->index for pages backing the bitmap file

The md driver allocates pages for storing the bitmap file data, which
are not page cache pages, and then stores the page granularity file
offset in page->index, which is a field that isn't really valid except
for page cache pages.

Use a separate index for the superblock, and use the scheme used at
read size to recalculate the index for the bitmap pages instead.

Signed-off-by: Christoph Hellwig <[e-mail]>
Signed-off-by: Song Liu <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

drivers/md/md-bitmap.c

···
 		    test_bit(Bitmap_sync, &rdev->flags))
 			continue;
 
-		if (sync_page_io(rdev, sector, iosize, page, REQ_OP_READ,
-				true)) {
-			page->index = index;
+		if (sync_page_io(rdev, sector, iosize, page, REQ_OP_READ, true))
 			return 0;
-		}
 	}
 	return -EIO;
 }
···
 }
 
 static int __write_sb_page(struct md_rdev *rdev, struct bitmap *bitmap,
-			   struct page *page)
+			   unsigned long pg_index, struct page *page)
 {
 	struct block_device *bdev;
 	struct mddev *mddev = bitmap->mddev;
 	struct bitmap_storage *store = &bitmap->storage;
 	loff_t sboff, offset = mddev->bitmap_info.offset;
-	sector_t ps, doff;
+	sector_t ps = pg_index * PAGE_SIZE / SECTOR_SIZE;
 	unsigned int size = PAGE_SIZE;
 	unsigned int opt_size = PAGE_SIZE;
+	sector_t doff;
 
 	bdev = (rdev->meta_bdev) ? rdev->meta_bdev : rdev->bdev;
-	if (page->index == store->file_pages - 1) {
+	if (pg_index == store->file_pages - 1) {
 		unsigned int last_page_size = store->bytes & (PAGE_SIZE - 1);
 
 		if (last_page_size == 0)
···
 		opt_size = optimal_io_size(bdev, last_page_size, size);
 	}
 
-	ps = page->index * PAGE_SIZE / SECTOR_SIZE;
 	sboff = rdev->sb_start + offset;
 	doff = rdev->data_offset;
 
···
 	return 0;
 }
 
-static void write_sb_page(struct bitmap *bitmap, struct page *page, int wait)
+static void write_sb_page(struct bitmap *bitmap, unsigned long pg_index,
+			  struct page *page, bool wait)
 {
 	struct mddev *mddev = bitmap->mddev;
 
···
 		struct md_rdev *rdev = NULL;
 
 		while ((rdev = next_active_rdev(rdev, mddev)) != NULL) {
-			if (__write_sb_page(rdev, bitmap, page) < 0) {
+			if (__write_sb_page(rdev, bitmap, pg_index, page) < 0) {
 				set_bit(BITMAP_WRITE_ERROR, &bitmap->flags);
 				return;
 			}
···
 		blk_cur++;
 		bh = bh->b_this_page;
 	}
-	page->index = index;
 
 	wait_event(bitmap->write_wait,
 		   atomic_read(&bitmap->pending_writes)==0);
···
 /*
  * write out a page to a file
  */
-static void write_page(struct bitmap *bitmap, struct page *page, int wait)
+static void filemap_write_page(struct bitmap *bitmap, unsigned long pg_index,
+			       bool wait)
 {
-	if (bitmap->storage.file)
+	struct bitmap_storage *store = &bitmap->storage;
+	struct page *page = store->filemap[pg_index];
+
+	if (mddev_is_clustered(bitmap->mddev)) {
+		pg_index += bitmap->cluster_slot *
+			DIV_ROUND_UP(store->bytes, PAGE_SIZE);
+	}
+
+	if (store->file)
 		write_file_page(bitmap, page, wait);
 	else
-		write_sb_page(bitmap, page, wait);
+		write_sb_page(bitmap, pg_index, page, wait);
 }
 
 /*
···
 	sb->sectors_reserved = cpu_to_le32(bitmap->mddev->
 					   bitmap_info.space);
 	kunmap_atomic(sb);
-	write_page(bitmap, bitmap->storage.sb_page, 1);
+
+	if (bitmap->storage.file)
+		write_file_page(bitmap, bitmap->storage.sb_page, 1);
+	else
+		write_sb_page(bitmap, bitmap->storage.sb_index,
+			      bitmap->storage.sb_page, 1);
 }
 EXPORT_SYMBOL(md_bitmap_update_sb);
 
···
 	bitmap->storage.sb_page = alloc_page(GFP_KERNEL | __GFP_ZERO);
 	if (bitmap->storage.sb_page == NULL)
 		return -ENOMEM;
-	bitmap->storage.sb_page->index = 0;
+	bitmap->storage.sb_index = 0;
 
 	sb = kmap_atomic(bitmap->storage.sb_page);
 
···
 	if (store->sb_page) {
 		store->filemap[0] = store->sb_page;
 		pnum = 1;
-		store->sb_page->index = offset;
+		store->sb_index = offset;
 	}
 
 	for ( ; pnum < num_pages; pnum++) {
···
 			store->file_pages = pnum;
 			return -ENOMEM;
 		}
-		store->filemap[pnum]->index = pnum + offset;
 	}
 	store->file_pages = pnum;
 
···
 	void *kaddr;
 	unsigned long chunk = block >> bitmap->counts.chunkshift;
 	struct bitmap_storage *store = &bitmap->storage;
+	unsigned long index = file_page_index(store, chunk);
 	unsigned long node_offset = 0;
 
 	if (mddev_is_clustered(bitmap->mddev))
···
 	else
 		set_bit_le(bit, kaddr);
 	kunmap_atomic(kaddr);
-	pr_debug("set file bit %lu page %lu\n", bit, page->index);
+	pr_debug("set file bit %lu page %lu\n", bit, index);
 	/* record page number so it gets flushed to disk when unplug occurs */
-	set_page_attr(bitmap, page->index - node_offset, BITMAP_PAGE_DIRTY);
+	set_page_attr(bitmap, index - node_offset, BITMAP_PAGE_DIRTY);
 }
 
 static void md_bitmap_file_clear_bit(struct bitmap *bitmap, sector_t block)
···
 	void *paddr;
 	unsigned long chunk = block >> bitmap->counts.chunkshift;
 	struct bitmap_storage *store = &bitmap->storage;
+	unsigned long index = file_page_index(store, chunk);
 	unsigned long node_offset = 0;
 
 	if (mddev_is_clustered(bitmap->mddev))
···
 	else
 		clear_bit_le(bit, paddr);
 	kunmap_atomic(paddr);
-	if (!test_page_attr(bitmap, page->index - node_offset, BITMAP_PAGE_NEEDWRITE)) {
-		set_page_attr(bitmap, page->index - node_offset, BITMAP_PAGE_PENDING);
+	if (!test_page_attr(bitmap, index - node_offset, BITMAP_PAGE_NEEDWRITE)) {
+		set_page_attr(bitmap, index - node_offset, BITMAP_PAGE_PENDING);
 		bitmap->allclean = 0;
 	}
 }
···
 							  "md bitmap_unplug");
 			}
 			clear_page_attr(bitmap, i, BITMAP_PAGE_PENDING);
-			write_page(bitmap, bitmap->storage.filemap[i], 0);
+			filemap_write_page(bitmap, i, false);
 			writing = 1;
 		}
 	}
···
 			memset(paddr + offset, 0xff, PAGE_SIZE - offset);
 			kunmap_atomic(paddr);
 
-			write_page(bitmap, page, 1);
+			filemap_write_page(bitmap, i, true);
 			if (test_bit(BITMAP_WRITE_ERROR, &bitmap->flags)) {
 				ret = -EIO;
 				goto err;
···
 			break;
 		if (bitmap->storage.filemap &&
 		    test_and_clear_page_attr(bitmap, j,
-					     BITMAP_PAGE_NEEDWRITE)) {
-			write_page(bitmap, bitmap->storage.filemap[j], 0);
-		}
+					     BITMAP_PAGE_NEEDWRITE))
+			filemap_write_page(bitmap, j, false);
 	}
 
  done:

drivers/md/md-bitmap.h

···
 		struct file *file;		/* backing disk file */
 		struct page *sb_page;		/* cached copy of the bitmap
 						 * file superblock */
+		unsigned long sb_index;
 		struct page **filemap;		/* list of cache pages for
 						 * the file */
 		unsigned long *filemap_attr;	/* attributes associated