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

[Haitao Shan <maillists.shan@xxxxxxxxx>]

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@xxxxxxxxx>

Signed-off-by: Wei Gang <gang.wei@xxxxxxxxx>

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);

Attachment: cpu_offline_mwait_fix.patch
Description: Binary data

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