diff --git a/kernel/console.c b/kernel/console.c
index 39415d6..05dc526 100644
--- a/kernel/console.c
+++ b/kernel/console.c
@@ -89,7 +89,7 @@ consoleread(int user_dst, uint64 dst, int n)
     // wait until interrupt handler has put some
     // input into cons.buffer.
     while(cons.r == cons.w){
-      if(myproc()->killed){
+      if(killed(myproc())){
         release(&cons.lock);
         return -1;
       }
diff --git a/kernel/defs.h b/kernel/defs.h
index 48641f5..7457b66 100644
--- a/kernel/defs.h
+++ b/kernel/defs.h
@@ -90,6 +90,8 @@ void            proc_mapstacks(pagetable_t);
 pagetable_t     proc_pagetable(struct proc *);
 void            proc_freepagetable(pagetable_t, uint64);
 int             kill(int);
+int             killed(struct proc*);
+void            setkilled(struct proc*);
 struct cpu*     mycpu(void);
 struct cpu*     getmycpu(void);
 struct proc*    myproc();
diff --git a/kernel/pipe.c b/kernel/pipe.c
index b6eefb9..f6b501a 100644
--- a/kernel/pipe.c
+++ b/kernel/pipe.c
@@ -81,7 +81,7 @@ pipewrite(struct pipe *pi, uint64 addr, int n)
 
   acquire(&pi->lock);
   while(i < n){
-    if(pi->readopen == 0 || pr->killed){
+    if(pi->readopen == 0 || killed(pr)){
       release(&pi->lock);
       return -1;
     }
@@ -111,7 +111,7 @@ piperead(struct pipe *pi, uint64 addr, int n)
 
   acquire(&pi->lock);
   while(pi->nread == pi->nwrite && pi->writeopen){  //DOC: pipe-empty
-    if(pr->killed){
+    if(killed(pr)){
       release(&pi->lock);
       return -1;
     }
diff --git a/kernel/proc.c b/kernel/proc.c
index 1ed3ee5..8d0ca8c 100644
--- a/kernel/proc.c
+++ b/kernel/proc.c
@@ -424,7 +424,7 @@ wait(uint64 addr)
     }
 
     // No point waiting if we don't have any children.
-    if(!havekids || p->killed){
+    if(!havekids || killed(p)){
       release(&wait_lock);
       return -1;
     }
@@ -603,6 +603,25 @@ kill(int pid)
   return -1;
 }
 
+void
+setkilled(struct proc *p)
+{
+  acquire(&p->lock);
+  p->killed = 1;
+  release(&p->lock);
+}
+
+int
+killed(struct proc *p)
+{
+  int k;
+  
+  acquire(&p->lock);
+  k = p->killed;
+  release(&p->lock);
+  return k;
+}
+
 // Copy to either a user address, or kernel address,
 // depending on usr_dst.
 // Returns 0 on success, -1 on error.
diff --git a/kernel/sysproc.c b/kernel/sysproc.c
index ecaa8cc..1de184e 100644
--- a/kernel/sysproc.c
+++ b/kernel/sysproc.c
@@ -58,7 +58,7 @@ sys_sleep(void)
   acquire(&tickslock);
   ticks0 = ticks;
   while(ticks - ticks0 < n){
-    if(myproc()->killed){
+    if(killed(myproc())){
       release(&tickslock);
       return -1;
     }
diff --git a/kernel/trap.c b/kernel/trap.c
index 524da44..512c850 100644
--- a/kernel/trap.c
+++ b/kernel/trap.c
@@ -53,7 +53,7 @@ usertrap(void)
   if(r_scause() == 8){
     // system call
 
-    if(p->killed)
+    if(killed(p))
       exit(-1);
 
     // sepc points to the ecall instruction,
@@ -70,10 +70,10 @@ usertrap(void)
   } else {
     printf("usertrap(): unexpected scause %p pid=%d\n", r_scause(), p->pid);
     printf("            sepc=%p stval=%p\n", r_sepc(), r_stval());
-    p->killed = 1;
+    setkilled(p);
   }
 
-  if(p->killed)
+  if(killed(p))
     exit(-1);
 
   // give up the CPU if this is a timer interrupt.