prevent stealing of process already chosen by another cpu

971c3376 · Nickolai Zeldovich · 394c7889 · 971c3376
--- a/proc.c
+++ b/proc.c
@@ -402,14 +402,16 @@ scheduler(void)

      acquire(&p->lock);

-      release(&runq->lock);
-
      // Switch to chosen process.  It is the process's job
      // to release proc->lock and then reacquire it
      // before jumping back to us.
      proc = p;
      switchuvm(p);
      p->state = RUNNING;
+
+      // Release runq lock only after setting RUNNING, to prevent stealing.
+      release(&runq->lock);
+
      mtrace_fcall_register(pid, 0, 0, mtrace_pause);
      mtrace_fcall_register(proc->pid, 0, 0, mtrace_resume);
      mtrace_call_set(1, cpunum());