Xen devel - Feb 2011 - [PATCH] Fixing mwait usage when doing cpu offline

Hi, Keir,

In debugging the issue "system hang when doing cpu offline", I
identified a
situation that could cause a dead lock. The scenario is:
mwait_idle_with_hint inside play_dead will access per cpu variable, which
causes #PF. The #PF handler will use printk, which will schedule a tasklet.
In scheduling a tasklet, per cpu variables are needed, otherwise, there will
be another #PF. These series of #PF produce a dead lock around tasklet_lock.

This patch avoids using per_cpu variable inside play_dead.

Signed-off-by: Shan Haitao <haitao.shan@intel.com>
Signed-off-by: Wei Gang <gang.wei@intel.com>

diff -r dac86c85222e xen/arch/x86/acpi/cpu_idle.c
--- a/xen/arch/x86/acpi/cpu_idle.c Fri Feb 18 19:07:11 2011 +0000
+++ b/xen/arch/x86/acpi/cpu_idle.c Wed Feb 23 17:05:32 2011 +0800
@@ -569,7 +569,8 @@ static void acpi_dead_idle(void)
         {
             case ACPI_CSTATE_EM_FFH:
                 /* Not treat interrupt as break event */
-                mwait_idle_with_hints(cx->address, 0);
+                __monitor((void *)&mwait_wakeup(smp_processor_id()), 0, 0);
+                __mwait(cx->address, 0);
                 break;
             case ACPI_CSTATE_EM_SYSIO:
                 inb(cx->address);



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