bcachefs: Fix data corruption on -ENOSPC in buffered write path

Found by generic/299: When we have to truncate a write due to -ENOSPC,
we may have to read in the folio we're writing to if we're now no longer
doing a complete write to a !uptodate folio.

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

diff --git a/fs/bcachefs/fs-io-buffered.c b/fs/bcachefs/fs-io-buffered.c
index 48a1ab9..9597280 100644 (file)
--- a/fs/bcachefs/fs-io-buffered.c
+++ b/fs/bcachefs/fs-io-buffered.c
@@ -856,6 +856,12 @@ static int __bch2_buffered_write(struct bch_inode_info *inode,
                                folios_trunc(&fs, fi);
                                end = min(end, folio_end_pos(darray_last(fs)));
                        } else {
+                               if (!folio_test_uptodate(f)) {
+                                       ret = bch2_read_single_folio(f, mapping);
+                                       if (ret)
+                                               goto out;
+                               }
+
                                folios_trunc(&fs, fi + 1);
                                end = f_pos + f_reserved;
                        }