From 72fef4f85513d200ca6b986b0bcc5c608142a1d6 Mon Sep 17 00:00:00 2001
From: rsc <rsc>
Date: Sun, 16 Jul 2006 02:09:45 +0000
Subject: [PATCH] Don't kill process when inside kernel.

---
 trap.c | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/trap.c b/trap.c
index 78a62f0..4c8a4bd 100644
--- a/trap.c
+++ b/trap.c
@@ -70,11 +70,18 @@ trap(struct Trapframe *tf)
     lapic_timerintr();
     if(cpus[cpu()].nlock)
       panic("timer interrupt while holding a lock");
+    if((read_eflags() & FL_IF) == 0)
+      panic("timer interrupt but interrupts now disabled");
     if(cp){
-      if((read_eflags() & FL_IF) == 0)
-        panic("timer interrupt but interrupts now disabled");
-      if(cp->killed)
+      // Force process exit if it has been killed
+      // and the interrupt came from user space.
+      // (If the kernel was executing at time of interrupt,
+      // don't kill the process.  Let the process get back
+      // out to its regular system call return.)
+      if((tf->tf_cs&3) == 3 && cp->killed)
         proc_exit();
+      
+      // Force process to give up CPU and let others run.
       if(cp->state == RUNNING)
         yield();
     }