From: Ben Pfaff <blp@cs.stanford.edu>
Date: Wed, 5 Apr 2006 19:25:49 +0000 (+0000)
Subject: Add comment to explain why we don't free initial_thread.
X-Git-Url: https://pintos-os.org/cgi-bin/gitweb.cgi?p=pintos-anon;a=commitdiff_plain;h=d07d499dd6655d15b274bb7713138dc9641a1fdb

Add comment to explain why we don't free initial_thread.
Thanks to Sunit Pal <sunit@stanford.edu> for the question.
---

diff --git a/src/threads/thread.c b/src/threads/thread.c
index 01e8ea4..16b8c8b 100644
--- a/src/threads/thread.c
+++ b/src/threads/thread.c
@@ -483,12 +483,13 @@ schedule_tail (struct thread *prev)
 
   /* If the thread we switched from is dying, destroy its struct
      thread.  This must happen late so that thread_exit() doesn't
-     pull out the rug under itself. */
-  if (prev != NULL && prev->status == THREAD_DYING) 
+     pull out the rug under itself.  (We don't free
+     initial_thread because its memory was not obtained via
+     palloc().) */
+  if (prev != NULL && prev->status == THREAD_DYING && prev != initial_thread) 
     {
       ASSERT (prev != cur);
-      if (prev != initial_thread)
-        palloc_free_page (prev);
+      palloc_free_page (prev);
     }
 }