soft page faults only when proc is not null

aad8c084 · Nickolai Zeldovich · 21fb8c30 · aad8c084
--- a/trap.c
+++ b/trap.c
@@ -47,13 +47,6 @@ trap(struct trapframe *tf)
    return;
  }

-  if(tf->trapno == T_PGFLT){
-    if(pagefault(proc->pgdir, proc->vmap, rcr2()) >= 0){
-      switchuvm(proc);
-      return;
-    }
-  }
-
  switch(tf->trapno){
  case T_IRQ0 + IRQ_TIMER:
    if(cpu->id == 0){
@@ -94,6 +87,14 @@ trap(struct trapframe *tf)
              tf->trapno, cpu->id, tf->eip, rcr2());
      panic("trap");
    }
+
+    if(tf->trapno == T_PGFLT){
+      if(pagefault(proc->pgdir, proc->vmap, rcr2()) >= 0){
+        switchuvm(proc);
+        return;
+      }
+    }
+
    // In user space, assume process misbehaved.
    cprintf("pid %d %s: trap %d err %d on cpu %d "
            "eip 0x%x addr 0x%x--kill proc\n",