[Xen-changelog] [xen-unstable] x86: Add warning comment explaining restrictions to play_dead().

[Xen patchbot-unstable <patchbot@xxxxxxx>]

# HG changeset patch
# User Shan Haitao <haitao.shan@xxxxxxxxx>
# Date 1299060115 0
# Node ID bde351b18fd0fce23e6d4ae24627ed15a9b7c768
# Parent  c5d121fd35c0451e8ae08749566c7fbbddb92706
x86: Add warning comment explaining restrictions to play_dead().

Signed-off-by: Shan Haitao <haitao.shan@xxxxxxxxx>
Signed-off-by: Keir Fraser <keir@xxxxxxx>
---


diff -r c5d121fd35c0 -r bde351b18fd0 xen/arch/x86/domain.c
--- a/xen/arch/x86/domain.c     Mon Feb 28 16:55:20 2011 +0000
+++ b/xen/arch/x86/domain.c     Wed Mar 02 10:01:55 2011 +0000
@@ -99,6 +99,15 @@
 
 static void play_dead(void)
 {
+    /*
+     * NOTE: After cpu_exit_clear, per-cpu variables are no longer accessible,
+     * as they may be freed at any time. In this case, heap corruption or
+     * #PF can occur (when heap debugging is enabled). For example, even
+     * printk() can involve tasklet scheduling, which touches per-cpu vars.
+     * 
+     * Consider very carefully when adding code to this path. Most hypervisor
+     * subsystems are unsafe to call.
+     */
     cpu_exit_clear(smp_processor_id());
     mb();
     local_irq_disable();

_______________________________________________
Xen-changelog mailing list
Xen-changelog@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-changelog