bcachefs: Don't overflow stack in bch2_extent_merge_inline()

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

fs/bcachefs/bkey.h

@@ -41,10 +41,7 @@ struct bkey_s {
 
 #define bkey_next(_k)		vstruct_next(_k)
 
-static inline unsigned bkey_val_u64s(const struct bkey *k)
-{
-	return k->u64s - BKEY_U64s;
-}
+#define bkey_val_u64s(_k)	((_k)->u64s - BKEY_U64s)
 
 static inline size_t bkey_val_bytes(const struct bkey *k)
 {

fs/bcachefs/extents.c

@@ -1651,6 +1651,10 @@ static bool bch2_extent_merge_inline(struct bch_fs *c,
 
 	EBUG_ON(bkey_written(b, m));
 
+	if (bkey_val_u64s(l) > BKEY_EXTENT_VAL_U64s_MAX ||
+	    bkey_val_u64s(r) > BKEY_EXTENT_VAL_U64s_MAX)
+		return BCH_MERGE_NOMERGE;
+
 	/*
 	 * We need to save copies of both l and r, because we might get a
 	 * partial merge (which modifies both) and then fails to repack