Index: sys/kern/kern_fork.c
===================================================================
--- sys/kern/kern_fork.c
+++ sys/kern/kern_fork.c
@@ -471,6 +471,7 @@
 	td2->td_sigstk = td->td_sigstk;
 	td2->td_flags = TDF_INMEM;
 	td2->td_lend_user_pri = PRI_MAX;
+	td2->td_pflags |= TDP_FORKING;
 
 #ifdef VIMAGE
 	td2->td_vnet = NULL;
@@ -1023,6 +1024,7 @@
 
 	if (p->p_sysent->sv_schedtail != NULL)
 		(p->p_sysent->sv_schedtail)(td);
+	td->td_pflags &= ~TDP_FORKING;
 }
 
 /*
Index: sys/sys/proc.h
===================================================================
--- sys/sys/proc.h
+++ sys/sys/proc.h
@@ -446,7 +446,7 @@
 #define	TDP_RESETSPUR	0x04000000 /* Reset spurious page fault history. */
 #define	TDP_NERRNO	0x08000000 /* Last errno is already in td_errno */
 #define	TDP_UIOHELD	0x10000000 /* Current uio has pages held in td_ma */
-#define	TDP_UNUSED29	0x20000000 /* --available-- */
+#define	TDP_FORKING	0x20000000 /* Thread is being created through fork() */
 #define	TDP_EXECVMSPC	0x40000000 /* Execve destroyed old vmspace */
 
 /*