iomap: clear the per-folio dirty bits on all writeback failures

write_cache_pages always clear the page dirty bit before calling into the
file systems, and leaves folios with a writeback failure without the
dirty bit after return.  We also clear the per-block writeback bits for
writeback failures unless no I/O has submitted, which will leave the
folio in an inconsistent state where it doesn't have the folio dirty,
but one or more per-block dirty bits.  This seems to be due the place
where the iomap_clear_range_dirty call was inserted into the existing
not very clearly structured code when adding per-block dirty bit support
and not actually intentional.  Switch to always clearing the dirty on
writeback failure.

Fixes: 4ce02c6 ("iomap: Add per-block dirty state tracking to improve performance")
Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20231207072710.176093-2-hch@lst.de
Signed-off-by: Christian Brauner <brauner@kernel.org>

Author: Christoph Hellwig

fs/iomap/buffered-io.c

@@ -1833,16 +1833,10 @@ iomap_writepage_map(struct iomap_writepage_ctx *wpc,
 	if (unlikely(error)) {
 		/*
 		 * Let the filesystem know what portion of the current page
-		 * failed to map. If the page hasn't been added to ioend, it
-		 * won't be affected by I/O completion and we must unlock it
-		 * now.
+		 * failed to map.
 		 */
 		if (wpc->ops->discard_folio)
 			wpc->ops->discard_folio(folio, pos);
-		if (!count) {
-			folio_unlock(folio);
-			goto done;
-		}
 	}
 
 	/*
@@ -1851,6 +1845,16 @@ iomap_writepage_map(struct iomap_writepage_ctx *wpc,
 	 * all the dirty bits in the folio here.
 	 */
 	iomap_clear_range_dirty(folio, 0, folio_size(folio));
+
+	/*
+	 * If the page hasn't been added to the ioend, it won't be affected by
+	 * I/O completion and we must unlock it now.
+	 */
+	if (error && !count) {
+		folio_unlock(folio);
+		goto done;
+	}
+
 	folio_start_writeback(folio);
 	folio_unlock(folio);