From 4087a6e7fc773ba4eb217dfc196dfe1eee84b25d Mon Sep 17 00:00:00 2001
From: Frans Kaashoek <kaashoek@mit.edu>
Date: Wed, 10 Aug 2022 20:35:42 -0400
Subject: [PATCH 1/4] Read and write p->killed using atomics

---
 kernel/console.c | 2 +-
 kernel/pipe.c    | 4 ++--
 kernel/proc.c    | 4 ++--
 kernel/sysproc.c | 2 +-
 kernel/trap.c    | 6 +++---
 5 files changed, 9 insertions(+), 9 deletions(-)

diff --git a/kernel/console.c b/kernel/console.c
index 23a2d35..b8fa1de 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(__sync_add_and_fetch(&(myproc()->killed), 0)){
         release(&cons.lock);
         return -1;
       }
diff --git a/kernel/pipe.c b/kernel/pipe.c
index b6eefb9..e438d7e 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 || __sync_add_and_fetch(&pr->killed,0)){
       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(__sync_add_and_fetch(&pr->killed,0)){
       release(&pi->lock);
       return -1;
     }
diff --git a/kernel/proc.c b/kernel/proc.c
index 2d0ffa1..221f0f8 100644
--- a/kernel/proc.c
+++ b/kernel/proc.c
@@ -422,7 +422,7 @@ wait(uint64 addr)
     }
 
     // No point waiting if we don't have any children.
-    if(!havekids || p->killed){
+    if(!havekids || __sync_add_and_fetch(&p->killed, 0)){
       release(&wait_lock);
       return -1;
     }
@@ -588,7 +588,7 @@ kill(int pid)
   for(p = proc; p < &proc[NPROC]; p++){
     acquire(&p->lock);
     if(p->pid == pid){
-      p->killed = 1;
+      __sync_bool_compare_and_swap(&p->killed, 0, 1);
       if(p->state == SLEEPING){
         // Wake process from sleep().
         p->state = RUNNABLE;
diff --git a/kernel/sysproc.c b/kernel/sysproc.c
index e8bcda9..61b715b 100644
--- a/kernel/sysproc.c
+++ b/kernel/sysproc.c
@@ -63,7 +63,7 @@ sys_sleep(void)
   acquire(&tickslock);
   ticks0 = ticks;
   while(ticks - ticks0 < n){
-    if(myproc()->killed){
+    if(__sync_add_and_fetch(&(myproc()->killed), 0)){
       release(&tickslock);
       return -1;
     }
diff --git a/kernel/trap.c b/kernel/trap.c
index 75fb3ec..b879f01 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(__sync_add_and_fetch(&p->killed, 0))
       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;
+    __sync_bool_compare_and_swap(&p->killed, 0, 1);
   }
 
-  if(p->killed)
+  if(__sync_add_and_fetch(&p->killed, 0))
     exit(-1);
 
   // give up the CPU if this is a timer interrupt.

From 975f3b31d3fac2c271df3107263df6ae454a98be Mon Sep 17 00:00:00 2001
From: Frans Kaashoek <kaashoek@mit.edu>
Date: Thu, 11 Aug 2022 07:23:17 -0400
Subject: [PATCH 2/4] Clean up using killed()

---
 kernel/console.c | 2 +-
 kernel/defs.h    | 1 +
 kernel/pipe.c    | 4 ++--
 kernel/proc.c    | 8 +++++++-
 kernel/sysproc.c | 2 +-
 kernel/trap.c    | 4 ++--
 6 files changed, 14 insertions(+), 7 deletions(-)

diff --git a/kernel/console.c b/kernel/console.c
index b8fa1de..d6eb209 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(__sync_add_and_fetch(&(myproc()->killed), 0)){
+      if(killed(myproc())){
         release(&cons.lock);
         return -1;
       }
diff --git a/kernel/defs.h b/kernel/defs.h
index 62b9292..7181d4d 100644
--- a/kernel/defs.h
+++ b/kernel/defs.h
@@ -90,6 +90,7 @@ void            proc_mapstacks(pagetable_t);
 pagetable_t     proc_pagetable(struct proc *);
 void            proc_freepagetable(pagetable_t, uint64);
 int             kill(int);
+int             killed(struct proc*);
 struct cpu*     mycpu(void);
 struct cpu*     getmycpu(void);
 struct proc*    myproc();
diff --git a/kernel/pipe.c b/kernel/pipe.c
index e438d7e..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 || __sync_add_and_fetch(&pr->killed,0)){
+    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(__sync_add_and_fetch(&pr->killed,0)){
+    if(killed(pr)){
       release(&pi->lock);
       return -1;
     }
diff --git a/kernel/proc.c b/kernel/proc.c
index 221f0f8..24680b6 100644
--- a/kernel/proc.c
+++ b/kernel/proc.c
@@ -422,7 +422,7 @@ wait(uint64 addr)
     }
 
     // No point waiting if we don't have any children.
-    if(!havekids || __sync_add_and_fetch(&p->killed, 0)){
+    if(!havekids || killed(p)){
       release(&wait_lock);
       return -1;
     }
@@ -601,6 +601,12 @@ kill(int pid)
   return -1;
 }
 
+int
+killed(struct proc *p)
+{
+  return __sync_add_and_fetch(&p->killed, 0);
+}
+
 // 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 61b715b..99a36a7 100644
--- a/kernel/sysproc.c
+++ b/kernel/sysproc.c
@@ -63,7 +63,7 @@ sys_sleep(void)
   acquire(&tickslock);
   ticks0 = ticks;
   while(ticks - ticks0 < n){
-    if(__sync_add_and_fetch(&(myproc()->killed), 0)){
+    if(killed(myproc())){
       release(&tickslock);
       return -1;
     }
diff --git a/kernel/trap.c b/kernel/trap.c
index b879f01..f895aea 100644
--- a/kernel/trap.c
+++ b/kernel/trap.c
@@ -53,7 +53,7 @@ usertrap(void)
   if(r_scause() == 8){
     // system call
 
-    if(__sync_add_and_fetch(&p->killed, 0))
+    if(killed(p))
       exit(-1);
 
     // sepc points to the ecall instruction,
@@ -73,7 +73,7 @@ usertrap(void)
     __sync_bool_compare_and_swap(&p->killed, 0, 1);
   }
 
-  if(__sync_add_and_fetch(&p->killed, 0))
+  if(killed(p))
     exit(-1);
 
   // give up the CPU if this is a timer interrupt.

From 429c7b717edd4c23d3666327986052b9b6eb29eb Mon Sep 17 00:00:00 2001
From: Frans Kaashoek <kaashoek@mit.edu>
Date: Thu, 11 Aug 2022 08:42:52 -0400
Subject: [PATCH 3/4] Use atomic store_n and load_n

---
 kernel/proc.c | 4 ++--
 kernel/trap.c | 2 +-
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/kernel/proc.c b/kernel/proc.c
index 24680b6..b4f8a80 100644
--- a/kernel/proc.c
+++ b/kernel/proc.c
@@ -588,7 +588,7 @@ kill(int pid)
   for(p = proc; p < &proc[NPROC]; p++){
     acquire(&p->lock);
     if(p->pid == pid){
-      __sync_bool_compare_and_swap(&p->killed, 0, 1);
+      __atomic_store_n(&p->killed, 1, __ATOMIC_SEQ_CST);
       if(p->state == SLEEPING){
         // Wake process from sleep().
         p->state = RUNNABLE;
@@ -604,7 +604,7 @@ kill(int pid)
 int
 killed(struct proc *p)
 {
-  return __sync_add_and_fetch(&p->killed, 0);
+  return  __atomic_load_n(&p->killed, __ATOMIC_SEQ_CST);
 }
 
 // Copy to either a user address, or kernel address,
diff --git a/kernel/trap.c b/kernel/trap.c
index f895aea..1039911 100644
--- a/kernel/trap.c
+++ b/kernel/trap.c
@@ -70,7 +70,7 @@ 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());
-    __sync_bool_compare_and_swap(&p->killed, 0, 1);
+    __atomic_store_n(&p->killed, 1, __ATOMIC_SEQ_CST);
   }
 
   if(killed(p))

From 4f716c8550b406c3e4b3e0c21b986ef99bc06c40 Mon Sep 17 00:00:00 2001
From: Frans Kaashoek <kaashoek@mit.edu>
Date: Thu, 11 Aug 2022 14:22:00 -0400
Subject: [PATCH 4/4] Use p->lock to read p->killed

---
 kernel/defs.h |  1 +
 kernel/proc.c | 17 +++++++++++++++--
 kernel/trap.c |  2 +-
 3 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/kernel/defs.h b/kernel/defs.h
index 7181d4d..e38ec00 100644
--- a/kernel/defs.h
+++ b/kernel/defs.h
@@ -91,6 +91,7 @@ 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/proc.c b/kernel/proc.c
index b4f8a80..5e37cb7 100644
--- a/kernel/proc.c
+++ b/kernel/proc.c
@@ -588,7 +588,7 @@ kill(int pid)
   for(p = proc; p < &proc[NPROC]; p++){
     acquire(&p->lock);
     if(p->pid == pid){
-      __atomic_store_n(&p->killed, 1, __ATOMIC_SEQ_CST);
+      p->killed = 1;
       if(p->state == SLEEPING){
         // Wake process from sleep().
         p->state = RUNNABLE;
@@ -601,10 +601,23 @@ kill(int pid)
   return -1;
 }
 
+void
+setkilled(struct proc *p)
+{
+  acquire(&p->lock);
+  p->killed = 1;
+  release(&p->lock);
+}
+
 int
 killed(struct proc *p)
 {
-  return  __atomic_load_n(&p->killed, __ATOMIC_SEQ_CST);
+  int k;
+  
+  acquire(&p->lock);
+  k = p->killed;
+  release(&p->lock);
+  return k;
 }
 
 // Copy to either a user address, or kernel address,
diff --git a/kernel/trap.c b/kernel/trap.c
index 1039911..44c9cdc 100644
--- a/kernel/trap.c
+++ b/kernel/trap.c
@@ -70,7 +70,7 @@ 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());
-    __atomic_store_n(&p->killed, 1, __ATOMIC_SEQ_CST);
+    setkilled(p);
   }
 
   if(killed(p))