afs: Fix waiting for writeback then skipping folio

Commit acc8d858 converted afs_writepages_region() to write back a
folio batch. The function waits for writeback to a folio, but then
proceeds to the rest of the batch without trying to write that folio
again. This patch fixes has it attempt to write the folio again.

[DH: Also remove an 'else' that adding a goto makes redundant]

Fixes: acc8d858 ("afs: convert afs_writepages_region() to use filemap_get_folios_tag()")
Signed-off-by: Vishal Moola (Oracle) <vishal.moola@gmail.com>
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Marc Dionne <marc.dionne@auristor.com>
cc: linux-afs@lists.infradead.org
Link: https://lore.kernel.org/r/20230607204120.89416-2-vishal.moola@gmail.com/

fs/afs/write.c

@@ -731,6 +731,7 @@ static int afs_writepages_region(struct address_space *mapping,
 			 * (changing page->mapping to NULL), or even swizzled
 			 * back from swapper_space to tmpfs file mapping
 			 */
+try_again:
 			if (wbc->sync_mode != WB_SYNC_NONE) {
 				ret = folio_lock_killable(folio);
 				if (ret < 0) {
@@ -757,9 +758,10 @@ static int afs_writepages_region(struct address_space *mapping,
 #ifdef CONFIG_AFS_FSCACHE
 					folio_wait_fscache(folio);
 #endif
-				} else {
-					start += folio_size(folio);
+					goto try_again;
 				}
+
+				start += folio_size(folio);
 				if (wbc->sync_mode == WB_SYNC_NONE) {
 					if (skips >= 5 || need_resched()) {
 						*_next = start;