Add atomic_fcmpset_int32 and some comments.

Because `atomic_fcmpset_int` maybe run not correctly sometimes, and then loop long time, But no reason found yet.

freebsd/amd64/include/atomic.h

@@ -227,6 +227,34 @@ atomic_fcmpset_##TYPE(volatile u_##TYPE *dst, u_##TYPE *expect, u_##TYPE src) \
 	return (res);					\
 }
 
+#ifdef FSTACK
+/*
+ * The atomic_fcmpset_int above run error sometimes,
+ * it's return value is 0 while CAS success, and then loop long time.
+ * And no reason found yet.
+ *
+ * But use the function can fix it.
+ * This function copied from DPDK's rte_atomic.h
+ */
+static __inline int					\
+atomic_fcmpset_int32(volatile u_int *dst, u_int *expect, u_int src) \
+{										\
+	u_char res;							\
+										\
+	__asm __volatile(					\
+	"	" MPLOCKED "		"			\
+	"cmpxchgl %[src], %[dst];"			\
+	"sete %[res];"						\
+	: [res] "=a" (res),     /* output */ \
+	  [dst] "=m" (*dst)					\
+	: [src] "r" (src),      /* input */	\
+	  "a" (*expect),					\
+	  "m" (*dst) 						\
+	: "memory");            /* no-clobber list */ \
+	return (res);						\
+}
+#endif
+
 ATOMIC_CMPSET(char);
 ATOMIC_CMPSET(short);
 ATOMIC_CMPSET(int);

freebsd/kern/kern_descrip.c

@@ -3136,6 +3136,16 @@ fget_unlocked_seq(struct filedesc *fdp, int fd, cap_rights_t *needrightsp,
  * if anything goes wrong. In practice this only happens when userspace is
  * racing with itself.
  */
+#ifdef FSTACK
+/*
+ * Note: If loop dead in this function,
+ *       Maybe CAS run not correctly in `refcount_acquire_if_not_zero`,
+ *       You can try modify `atomic_fcmpset_int` to `atomic_fcmpset_int32`
+ *       in function `refcount_acquire_if_gt` of `refcount.h`
+ *
+ *      See also `atomic_fcmpset_int32` in `freebsd/amd64/include/atomic.h`
+ */
+#endif
 int
 fget_unlocked(struct filedesc *fdp, int fd, cap_rights_t *needrightsp,
     struct file **fpp)
@@ -5137,7 +5147,7 @@ ff_getmaxfd(void)
 {
 	struct thread *td = curthread;
 	return 	getmaxfd(td);
-	
+
 }
 
 #endif

freebsd/sys/refcount.h

@@ -117,6 +117,15 @@ refcount_acquire_checked(volatile u_int *count)
  * This functions returns non-zero if the refcount was
  * incremented. Else zero is returned.
  */
+#ifdef FSTACK
+/*
+ * Note: If loop dead in this function,
+ *       Maybe CAS that atomic_fcmpset_int run not correctly in this function,
+ *       You can try modify `atomic_fcmpset_int` to `atomic_fcmpset_int32`.
+ *
+ *      See also `atomic_fcmpset_int32` in `freebsd/amd64/include/atomic.h`
+ */
+#endif
 static __inline __result_use_check bool
 refcount_acquire_if_gt(volatile u_int *count, u_int n)
 {