jbd2: replace obvious uses of b_page with b_folio

These places just use b_page to get to the buffer's address_space or have
already been converted to folio.

Link: https://lkml.kernel.org/r/20221215214402.3522366-10-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

fs/jbd2/commit.c

@@ -63,16 +63,12 @@ static void journal_end_buffer_io_sync(struct buffer_head *bh, int uptodate)
 static void release_buffer_page(struct buffer_head *bh)
 {
 	struct folio *folio;
-	struct page *page;
 
 	if (buffer_dirty(bh))
 		goto nope;
 	if (atomic_read(&bh->b_count) != 1)
 		goto nope;
-	page = bh->b_page;
-	if (!page)
-		goto nope;
-	folio = page_folio(page);
+	folio = bh->b_folio;
 	if (folio->mapping)
 		goto nope;
 
@@ -1040,7 +1036,7 @@ void jbd2_journal_commit_transaction(journal_t *journal)
 			 * already detached from the mapping and buffers cannot
 			 * get reused.
 			 */
-			mapping = READ_ONCE(bh->b_page->mapping);
+			mapping = READ_ONCE(bh->b_folio->mapping);
 			if (mapping && !sb_is_blkdev_sb(mapping->host->i_sb)) {
 				clear_buffer_mapped(bh);
 				clear_buffer_new(bh);

fs/jbd2/journal.c

@@ -2938,7 +2938,7 @@ struct journal_head *jbd2_journal_add_journal_head(struct buffer_head *bh)
 	} else {
 		J_ASSERT_BH(bh,
 			(atomic_read(&bh->b_count) > 0) ||
-			(bh->b_page && bh->b_page->mapping));
+			(bh->b_folio && bh->b_folio->mapping));
 
 		if (!new_jh) {
 			jbd_unlock_bh_journal_head(bh);