From 0498bfd15937d64599b8c63948907a8b60e5d6ae Mon Sep 17 00:00:00 2001
From: Robert Morris <rtm@csail.mit.edu>
Date: Mon, 1 Jul 2019 13:46:11 -0400
Subject: timer interrupt in the kernel -> yield

---
 kernel/kernelvec.S |  2 +-
 kernel/trap.c      | 17 ++++++++++++++---
 2 files changed, 15 insertions(+), 4 deletions(-)

(limited to 'kernel')

diff --git a/kernel/kernelvec.S b/kernel/kernelvec.S
index 4f52688..e9b0ced 100644
--- a/kernel/kernelvec.S
+++ b/kernel/kernelvec.S
@@ -47,7 +47,7 @@ kernelvec:
         ld ra, 0(sp)
         ld sp, 8(sp)
         ld gp, 16(sp)
-        ld tp, 24(sp)
+        // not this, in case we moved CPUs: ld tp, 24(sp)
         ld t0, 32(sp)
         ld t1, 40(sp)
         ld t2, 48(sp)
diff --git a/kernel/trap.c b/kernel/trap.c
index 586f123..06fc4b3 100644
--- a/kernel/trap.c
+++ b/kernel/trap.c
@@ -121,12 +121,14 @@ usertrapret(void)
   ((void (*)(uint64,uint64))TRAMPOLINE)(TRAMPOLINE - PGSIZE, satp);
 }
 
-// interrupts and exceptions from kernel code go here,
+// interrupts and exceptions from kernel code go here via kernelvec,
 // on whatever the current kernel stack is.
 // must be 4-byte aligned to fit in stvec.
 void 
 kerneltrap()
 {
+  int which_dev = 0;
+  uint64 sepc = r_sepc();
   uint64 sstatus = r_sstatus();
   uint64 scause = r_scause();
   
@@ -135,11 +137,20 @@ kerneltrap()
   if(intr_get() != 0)
     panic("kerneltrap: interrupts enabled");
 
-  if(devintr() == 0){
-    printf("scause 0x%p\n", scause);
+  if((which_dev = devintr()) == 0){
+    printf("scause %p\n", scause);
     printf("sepc=%p stval=%p\n", r_sepc(), r_stval());
     panic("kerneltrap");
   }
+
+  // give up the CPU if this is a timer interrupt.
+  if(which_dev == 2 && myproc() != 0 && myproc()->state == RUNNING)
+    yield();
+
+  // the yield() may have caused some traps to occur,
+  // so restore trap registers for use by kernelvec.S's sepc instruction.
+  w_sepc(sepc);
+  w_sstatus(sstatus);
 }
 
 // check if it's an external interrupt or software interrupt,
-- 
cgit v1.2.3


From 9b99f007434ea3af0c4834a91f19952d5670e16b Mon Sep 17 00:00:00 2001
From: Robert Morris <rtm@csail.mit.edu>
Date: Mon, 1 Jul 2019 14:15:18 -0400
Subject: oops, don't hold mycpu() result across intr_off()

---
 kernel/spinlock.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

(limited to 'kernel')

diff --git a/kernel/spinlock.c b/kernel/spinlock.c
index 557a86c..5a44a46 100644
--- a/kernel/spinlock.c
+++ b/kernel/spinlock.c
@@ -87,13 +87,12 @@ holding(struct spinlock *lk)
 void
 push_off(void)
 {
-  struct cpu *c = mycpu();
   int old = intr_get();
 
   intr_off();
-  if(c->noff == 0)
-    c->intena = old;
-  c->noff += 1;
+  if(mycpu()->noff == 0)
+    mycpu()->intena = old;
+  mycpu()->noff += 1;
 }
 
 void
-- 
cgit v1.2.3


From 18e76a6c47b0f62b2458430d4357f3eb68bfd759 Mon Sep 17 00:00:00 2001
From: Robert Morris <rtm@csail.mit.edu>
Date: Mon, 1 Jul 2019 17:01:50 -0400
Subject: sbrk() returns a pointer, so it should be 64 bits

---
 kernel/syscall.c | 46 +++++++++++++++++++++++-----------------------
 kernel/sysfile.c | 26 +++++++++++++-------------
 kernel/sysproc.c | 16 ++++++++--------
 3 files changed, 44 insertions(+), 44 deletions(-)

(limited to 'kernel')

diff --git a/kernel/syscall.c b/kernel/syscall.c
index ca34f2c..ff10f9c 100644
--- a/kernel/syscall.c
+++ b/kernel/syscall.c
@@ -116,29 +116,29 @@ argstr(int n, char *buf, int max)
   return fetchstr(addr, buf, max);
 }
 
-extern int sys_chdir(void);
-extern int sys_close(void);
-extern int sys_dup(void);
-extern int sys_exec(void);
-extern int sys_exit(void);
-extern int sys_fork(void);
-extern int sys_fstat(void);
-extern int sys_getpid(void);
-extern int sys_kill(void);
-extern int sys_link(void);
-extern int sys_mkdir(void);
-extern int sys_mknod(void);
-extern int sys_open(void);
-extern int sys_pipe(void);
-extern int sys_read(void);
-extern int sys_sbrk(void);
-extern int sys_sleep(void);
-extern int sys_unlink(void);
-extern int sys_wait(void);
-extern int sys_write(void);
-extern int sys_uptime(void);
-
-static int (*syscalls[])(void) = {
+extern uint64 sys_chdir(void);
+extern uint64 sys_close(void);
+extern uint64 sys_dup(void);
+extern uint64 sys_exec(void);
+extern uint64 sys_exit(void);
+extern uint64 sys_fork(void);
+extern uint64 sys_fstat(void);
+extern uint64 sys_getpid(void);
+extern uint64 sys_kill(void);
+extern uint64 sys_link(void);
+extern uint64 sys_mkdir(void);
+extern uint64 sys_mknod(void);
+extern uint64 sys_open(void);
+extern uint64 sys_pipe(void);
+extern uint64 sys_read(void);
+extern uint64 sys_sbrk(void);
+extern uint64 sys_sleep(void);
+extern uint64 sys_unlink(void);
+extern uint64 sys_wait(void);
+extern uint64 sys_write(void);
+extern uint64 sys_uptime(void);
+
+static uint64 (*syscalls[])(void) = {
 [SYS_fork]    sys_fork,
 [SYS_exit]    sys_exit,
 [SYS_wait]    sys_wait,
diff --git a/kernel/sysfile.c b/kernel/sysfile.c
index 7788de3..77e273f 100644
--- a/kernel/sysfile.c
+++ b/kernel/sysfile.c
@@ -52,7 +52,7 @@ fdalloc(struct file *f)
   return -1;
 }
 
-int
+uint64
 sys_dup(void)
 {
   struct file *f;
@@ -66,7 +66,7 @@ sys_dup(void)
   return fd;
 }
 
-int
+uint64
 sys_read(void)
 {
   struct file *f;
@@ -78,7 +78,7 @@ sys_read(void)
   return fileread(f, p, n);
 }
 
-int
+uint64
 sys_write(void)
 {
   struct file *f;
@@ -91,7 +91,7 @@ sys_write(void)
   return filewrite(f, p, n);
 }
 
-int
+uint64
 sys_close(void)
 {
   int fd;
@@ -104,7 +104,7 @@ sys_close(void)
   return 0;
 }
 
-int
+uint64
 sys_fstat(void)
 {
   struct file *f;
@@ -116,7 +116,7 @@ sys_fstat(void)
 }
 
 // Create the path new as a link to the same inode as old.
-int
+uint64
 sys_link(void)
 {
   char name[DIRSIZ], new[MAXPATH], old[MAXPATH];
@@ -182,7 +182,7 @@ isdirempty(struct inode *dp)
 }
 
 //PAGEBREAK!
-int
+uint64
 sys_unlink(void)
 {
   struct inode *ip, *dp;
@@ -284,7 +284,7 @@ create(char *path, short type, short major, short minor)
   return ip;
 }
 
-int
+uint64
 sys_open(void)
 {
   char path[MAXPATH];
@@ -347,7 +347,7 @@ sys_open(void)
   return fd;
 }
 
-int
+uint64
 sys_mkdir(void)
 {
   char path[MAXPATH];
@@ -363,7 +363,7 @@ sys_mkdir(void)
   return 0;
 }
 
-int
+uint64
 sys_mknod(void)
 {
   struct inode *ip;
@@ -383,7 +383,7 @@ sys_mknod(void)
   return 0;
 }
 
-int
+uint64
 sys_chdir(void)
 {
   char path[MAXPATH];
@@ -408,7 +408,7 @@ sys_chdir(void)
   return 0;
 }
 
-int
+uint64
 sys_exec(void)
 {
   char path[MAXPATH], *argv[MAXARG];
@@ -446,7 +446,7 @@ sys_exec(void)
   return ret;
 }
 
-int
+uint64
 sys_pipe(void)
 {
   uint64 fdarray; // user pointer to array of two integers
diff --git a/kernel/sysproc.c b/kernel/sysproc.c
index e57e045..93ea9bc 100644
--- a/kernel/sysproc.c
+++ b/kernel/sysproc.c
@@ -6,32 +6,32 @@
 #include "memlayout.h"
 #include "proc.h"
 
-int
+uint64
 sys_exit(void)
 {
   exit();
   return 0;  // not reached
 }
 
-int
+uint64
 sys_getpid(void)
 {
   return myproc()->pid;
 }
 
-int
+uint64
 sys_fork(void)
 {
   return fork();
 }
 
-int
+uint64
 sys_wait(void)
 {
   return wait();
 }
 
-int
+uint64
 sys_sbrk(void)
 {
   int addr;
@@ -45,7 +45,7 @@ sys_sbrk(void)
   return addr;
 }
 
-int
+uint64
 sys_sleep(void)
 {
   int n;
@@ -66,7 +66,7 @@ sys_sleep(void)
   return 0;
 }
 
-int
+uint64
 sys_kill(void)
 {
   int pid;
@@ -78,7 +78,7 @@ sys_kill(void)
 
 // return how many clock tick interrupts have occurred
 // since start.
-int
+uint64
 sys_uptime(void)
 {
   uint xticks;
-- 
cgit v1.2.3


From abfe9999f447c15d904b3c11f32d4a22a45470a0 Mon Sep 17 00:00:00 2001
From: Robert Morris <rtm@csail.mit.edu>
Date: Mon, 1 Jul 2019 17:46:06 -0400
Subject: have fork() fail, not panic, if not enough phys mem

---
 kernel/defs.h |  2 +-
 kernel/proc.c | 42 +++++++++++++++++++++++++++++-------------
 kernel/vm.c   | 11 +++++++++--
 3 files changed, 39 insertions(+), 16 deletions(-)

(limited to 'kernel')

diff --git a/kernel/defs.h b/kernel/defs.h
index 1b397fe..1c0b39a 100644
--- a/kernel/defs.h
+++ b/kernel/defs.h
@@ -185,7 +185,7 @@ pagetable_t     uvmcreate(void);
 void            uvminit(pagetable_t, uchar *, uint);
 uint64          uvmalloc(pagetable_t, uint64, uint64);
 uint64          uvmdealloc(pagetable_t, uint64, uint64);
-void            uvmcopy(pagetable_t, pagetable_t, uint64);
+int            uvmcopy(pagetable_t, pagetable_t, uint64);
 void            uvmfree(pagetable_t, uint64);
 void            mappages(pagetable_t, uint64, uint64, uint64, int);
 void            unmappages(pagetable_t, uint64, uint64, int);
diff --git a/kernel/proc.c b/kernel/proc.c
index 4ae34c8..e0ee965 100644
--- a/kernel/proc.c
+++ b/kernel/proc.c
@@ -109,6 +109,28 @@ found:
   return p;
 }
 
+// free a proc structure and the data hanging from it,
+// including user pages.
+// the proc lock must be held.
+static void
+freeproc(struct proc *p)
+{
+  if(p->kstack)
+    kfree(p->kstack);
+  p->kstack = 0;
+  if(p->tf)
+    kfree((void*)p->tf);
+  p->tf = 0;
+  if(p->pagetable)
+    proc_freepagetable(p->pagetable, p->sz);
+  p->pagetable = 0;
+  p->pid = 0;
+  p->parent = 0;
+  p->name[0] = 0;
+  p->killed = 0;
+  p->state = UNUSED;
+}
+
 // Create a page table for a given process,
 // with no users pages, but with trampoline pages.
 // Called both when creating a process, and
@@ -145,7 +167,8 @@ proc_freepagetable(pagetable_t pagetable, uint64 sz)
 {
   unmappages(pagetable, TRAMPOLINE, PGSIZE, 0);
   unmappages(pagetable, TRAMPOLINE-PGSIZE, PGSIZE, 0);
-  uvmfree(pagetable, sz);
+  if(sz > 0)
+    uvmfree(pagetable, sz);
 }
 
 // a user program that calls exec("/init")
@@ -223,7 +246,10 @@ fork(void)
   }
 
   // Copy user memory from parent to child.
-  uvmcopy(p->pagetable, np->pagetable, p->sz);
+  if(uvmcopy(p->pagetable, np->pagetable, p->sz) < 0){
+    freeproc(np);
+    return -1;
+  }
   np->sz = p->sz;
 
   np->parent = p;
@@ -319,17 +345,7 @@ wait(void)
       if(np->state == ZOMBIE){
         // Found one.
         pid = np->pid;
-        kfree(np->kstack);
-        np->kstack = 0;
-        kfree((void*)np->tf);
-        np->tf = 0;
-        proc_freepagetable(np->pagetable, np->sz);
-        np->pagetable = 0;
-        np->pid = 0;
-        np->parent = 0;
-        np->name[0] = 0;
-        np->killed = 0;
-        np->state = UNUSED;
+        freeproc(np);
         release(&ptable.lock);
         return pid;
       }
diff --git a/kernel/vm.c b/kernel/vm.c
index 580669f..7d67464 100644
--- a/kernel/vm.c
+++ b/kernel/vm.c
@@ -273,7 +273,9 @@ uvmfree(pagetable_t pagetable, uint64 sz)
 // its memory into a child's page table.
 // Copies both the page table and the
 // physical memory.
-void
+// returns 0 on success, -1 on failure.
+// frees any allocated pages on failure.
+int
 uvmcopy(pagetable_t old, pagetable_t new, uint64 sz)
 {
   pte_t *pte;
@@ -289,10 +291,15 @@ uvmcopy(pagetable_t old, pagetable_t new, uint64 sz)
     pa = PTE2PA(*pte);
     flags = PTE_FLAGS(*pte);
     if((mem = kalloc()) == 0)
-      panic("uvmcopy: kalloc failed");
+      goto err;
     memmove(mem, (char*)pa, PGSIZE);
     mappages(new, i, PGSIZE, (uint64)mem, flags);
   }
+  return 0;
+
+ err:
+  unmappages(new, 0, i, 1);
+  return -1;
 }
 
 // Copy from kernel to user.
-- 
cgit v1.2.3


From 40f1041a0a7cd8a1902371cf459989c19f1dc718 Mon Sep 17 00:00:00 2001
From: Robert Morris <rtm@csail.mit.edu>
Date: Tue, 2 Jul 2019 05:20:11 -0400
Subject: don't enable interrupts until done with sstatus, scause, &c

---
 kernel/trap.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

(limited to 'kernel')

diff --git a/kernel/trap.c b/kernel/trap.c
index 06fc4b3..835a3b0 100644
--- a/kernel/trap.c
+++ b/kernel/trap.c
@@ -37,7 +37,7 @@ void
 usertrap(void)
 {
   int which_dev = 0;
-  
+
   if((r_sstatus() & SSTATUS_SPP) != 0)
     panic("usertrap: not from user mode");
 
@@ -49,8 +49,6 @@ usertrap(void)
   
   // save user program counter.
   p->tf->epc = r_sepc();
-
-  intr_on();
   
   if(r_scause() == 8){
     // system call
@@ -59,11 +57,15 @@ usertrap(void)
     // but we want to return to the next instruction.
     p->tf->epc += 4;
 
+    // an interrupt will change sstatus &c registers,
+    // so don't enable until done with those registers.
+    intr_on();
+
     syscall();
   } else if((which_dev = devintr()) != 0){
     // ok
   } else {
-    printf("usertrap(): unexpected scause 0x%p pid=%d\n", r_scause(), p->pid);
+    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;
   }
-- 
cgit v1.2.3


From 1540c8b15ac35de9027e60804a786d23703d383d Mon Sep 17 00:00:00 2001
From: Robert Morris <rtm@csail.mit.edu>
Date: Tue, 2 Jul 2019 11:04:35 -0400
Subject: COW tests

---
 kernel/vm.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

(limited to 'kernel')

diff --git a/kernel/vm.c b/kernel/vm.c
index 7d67464..d5ff594 100644
--- a/kernel/vm.c
+++ b/kernel/vm.c
@@ -97,8 +97,8 @@ walk(pagetable_t pagetable, uint64 va, int alloc)
 }
 
 // Look up a virtual address, return the physical address,
-// Can only be used to look up user pages.
 // or 0 if not mapped.
+// Can only be used to look up user pages.
 uint64
 walkaddr(pagetable_t pagetable, uint64 va)
 {
-- 
cgit v1.2.3


From b27f275014cb473960b9e4d36b03455e404116a7 Mon Sep 17 00:00:00 2001
From: Robert Morris <rtm@csail.mit.edu>
Date: Tue, 2 Jul 2019 11:17:50 -0400
Subject: avoid allocproc() returning a struct proc with non-zero p->sz

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

(limited to 'kernel')

diff --git a/kernel/proc.c b/kernel/proc.c
index e0ee965..20d5085 100644
--- a/kernel/proc.c
+++ b/kernel/proc.c
@@ -124,9 +124,11 @@ freeproc(struct proc *p)
   if(p->pagetable)
     proc_freepagetable(p->pagetable, p->sz);
   p->pagetable = 0;
+  p->sz = 0;
   p->pid = 0;
   p->parent = 0;
   p->name[0] = 0;
+  p->chan = 0;
   p->killed = 0;
   p->state = UNUSED;
 }
-- 
cgit v1.2.3


From f59c1bf1d82da4b445c1cff10c228ea55fa035d4 Mon Sep 17 00:00:00 2001
From: Robert Morris <rtm@csail.mit.edu>
Date: Tue, 2 Jul 2019 11:45:06 -0400
Subject: try to continue from walk() failing to allocate a page-table page

---
 kernel/defs.h |  4 ++--
 kernel/vm.c   | 19 ++++++++++++++-----
 2 files changed, 16 insertions(+), 7 deletions(-)

(limited to 'kernel')

diff --git a/kernel/defs.h b/kernel/defs.h
index 1c0b39a..bd89af0 100644
--- a/kernel/defs.h
+++ b/kernel/defs.h
@@ -185,9 +185,9 @@ pagetable_t     uvmcreate(void);
 void            uvminit(pagetable_t, uchar *, uint);
 uint64          uvmalloc(pagetable_t, uint64, uint64);
 uint64          uvmdealloc(pagetable_t, uint64, uint64);
-int            uvmcopy(pagetable_t, pagetable_t, uint64);
+int             uvmcopy(pagetable_t, pagetable_t, uint64);
 void            uvmfree(pagetable_t, uint64);
-void            mappages(pagetable_t, uint64, uint64, uint64, int);
+int             mappages(pagetable_t, uint64, uint64, uint64, int);
 void            unmappages(pagetable_t, uint64, uint64, int);
 uint64          walkaddr(pagetable_t, uint64);
 int             copyout(pagetable_t, uint64, char *, uint64);
diff --git a/kernel/vm.c b/kernel/vm.c
index d5ff594..bdb53c2 100644
--- a/kernel/vm.c
+++ b/kernel/vm.c
@@ -119,8 +119,9 @@ walkaddr(pagetable_t pagetable, uint64 va)
 
 // Create PTEs for virtual addresses starting at va that refer to
 // physical addresses starting at pa. va and size might not
-// be page-aligned.
-void
+// be page-aligned. Returns 0 on success, -1 if walk() couldn't
+// allocate a needed page-table page.
+int
 mappages(pagetable_t pagetable, uint64 va, uint64 size, uint64 pa, int perm)
 {
   uint64 a, last;
@@ -130,7 +131,7 @@ mappages(pagetable_t pagetable, uint64 va, uint64 size, uint64 pa, int perm)
   last = PGROUNDDOWN(va + size - 1);
   for(;;){
     if((pte = walk(pagetable, a, 1)) == 0)
-      panic("mappages: walk");
+      return -1;
     if(*pte & PTE_V)
       panic("remap");
     *pte = PA2PTE(pa) | perm | PTE_V;
@@ -139,6 +140,7 @@ mappages(pagetable_t pagetable, uint64 va, uint64 size, uint64 pa, int perm)
     a += PGSIZE;
     pa += PGSIZE;
   }
+  return 0;
 }
 
 // Remove mappings from a page table. The mappings in
@@ -222,7 +224,11 @@ uvmalloc(pagetable_t pagetable, uint64 oldsz, uint64 newsz)
       return 0;
     }
     memset(mem, 0, PGSIZE);
-    mappages(pagetable, a, PGSIZE, (uint64)mem, PTE_W|PTE_X|PTE_R|PTE_U);
+    if(mappages(pagetable, a, PGSIZE, (uint64)mem, PTE_W|PTE_X|PTE_R|PTE_U) != 0){
+      kfree(mem);
+      uvmdealloc(pagetable, a, oldsz);
+      return 0;
+    }
   }
   return newsz;
 }
@@ -293,7 +299,10 @@ uvmcopy(pagetable_t old, pagetable_t new, uint64 sz)
     if((mem = kalloc()) == 0)
       goto err;
     memmove(mem, (char*)pa, PGSIZE);
-    mappages(new, i, PGSIZE, (uint64)mem, flags);
+    if(mappages(new, i, PGSIZE, (uint64)mem, flags) != 0){
+      kfree(mem);
+      goto err;
+    }
   }
   return 0;
 
-- 
cgit v1.2.3