bcachefs: Convert a BUG_ON() to a warning

We shouldn't ever be writing past i_size - but, apparently there's still
a bug to track down.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/fs-io.c

@@ -757,6 +757,9 @@ static void bch2_set_page_dirty(struct bch_fs *c,
 	struct bch_page_state *s = bch2_page_state(page);
 	unsigned i, dirty_sectors = 0;
 
+	WARN_ON(page_offset(page) + offset + len >
+		round_up(i_size_read(&inode->v), block_bytes(c)));
+
 	for (i = round_down(offset, block_bytes(c)) >> 9;
 	     i < round_up(offset + len, block_bytes(c)) >> 9;
 	     i++) {
@@ -1442,7 +1445,7 @@ static int __bch2_writepage(struct folio *folio,
 				     sectors << 9, offset << 9));
 
 		/* Check for writing past i_size: */
-		BUG_ON((bio_end_sector(&w->io->op.op.wbio.bio) << 9) >
+		WARN_ON((bio_end_sector(&w->io->op.op.wbio.bio) << 9) >
 			round_up(i_size, block_bytes(c)));
 
 		w->io->op.op.res.sectors += reserved_sectors;