From c4f6a241cdc220dafe01bc7ca2ca7f8a253a838c Mon Sep 17 00:00:00 2001
From: Robert Morris <rtm@csail.mit.edu>
Date: Sun, 7 Jul 2019 07:03:28 -0400
Subject: [PATCH] avoid a double-lock of initproc->lock if child of init is
 reparenting

---
 kernel/proc.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/kernel/proc.c b/kernel/proc.c
index 2266ca6..cfb3262 100644
--- a/kernel/proc.c
+++ b/kernel/proc.c
@@ -292,6 +292,7 @@ fork(void)
 // are locked.
 void reparent(struct proc *p, struct proc *parent) {
   struct proc *pp;
+  int init_is_my_parent = (p->parent == initproc);
 
   for(pp = ptable.proc; pp < &ptable.proc[NPROC]; pp++){
     if (pp != p && pp != parent) {
@@ -299,9 +300,11 @@ void reparent(struct proc *p, struct proc *parent) {
       if(pp->parent == p){
         pp->parent = initproc;
         if(pp->state == ZOMBIE) {
-          acquire(&initproc->lock);
+          if(!init_is_my_parent)
+            acquire(&initproc->lock);
           wakeup1(initproc);
-          release(&initproc->lock);
+          if(!init_is_my_parent)
+            release(&initproc->lock);
         }
       }
       release(&pp->lock);