Xen devel - Mar 2011 - [Patch] Add comments of code restrictions inside play_dead()

This patch adds comments inside play_dead. This can be served as a notice
to developers who will add code to this code path.

Signed-off-by: Shan Haitao <haitao.shan@intel.com>

diff -r c5d121fd35c0 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 Tue Mar 01 16:03:40 2011 +0800
@@ -99,6 +99,14 @@ static void default_dead_idle(void)

 static void play_dead(void)
 {
+    /*
+     * Important note:
+     *   After cpu_exit_clear, one can never assume per cpu variables are
+     * still accessable. Otherwise, #PF will happen. For example, calling
to
+     * printk() will involve tasklet scheduling ,which also touches per cpu
+     * variables.
+     * Consider more carefully when adding code to this path.
+     */
     cpu_exit_clear(smp_processor_id());
     mb();
     local_irq_disable();



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