Re: [Xen-devel] [PATCH] serialize suspend-resume process

[BVK Chaitanya <bayapuneni_chaitanya@xxxxxxxxxxxx>]

Hi Keir,

diff -r 44e3ace9a1f1 drivers/xen/core/reboot.c
--- a/drivers/xen/core/reboot.c Thu Jul 31 09:46:58 2008 +0100
+++ b/drivers/xen/core/reboot.c Fri Aug 01 04:14:43 2008 +0530
@@ -108,6 +116,31 @@ static int xen_suspend(void *__unused)
        return 0;
 }

+static void switch_shutdown_state(int new_state)
+{
+       int prev_state, old_state = SHUTDOWN_INVALID;
+
+       /* We only drive shutdown_state into an active state. */
+       if (new_state == SHUTDOWN_INVALID)
+               return;
+
+       do {
+               /* We drop this transition if already in an active state. */
+               if ((old_state != SHUTDOWN_INVALID) &&
+                   (old_state != SHUTDOWN_RESUMING))
+                       return;
+               /* Attempt to transition. */
+               prev_state = old_state;
+               old_state = cmpxchg(&shutting_down, old_state, new_state);
+       } while (old_state != prev_state);
+
+       /* Either we kick off the work, or we leave it to xen_suspend(). */
+       if (old_state == SHUTDOWN_INVALID)
+               schedule_work(&shutdown_work);
+       else
+               BUG_ON(old_state != SHUTDOWN_RESUMING);
+}
+
 static void __shutdown_handler(void *unused)
 {
        int err;



It is doing a busy-wait loop till suspend-resume cycle completes, if 
any.  I found that it may go more than 25 msec sometimes.



@@ -220,26 +247,24 @@ static struct xenbus_watch sysrq_watch =

 static irqreturn_t suspend_int(int irq, void* dev_id, struct pt_regs 
*ptregs)
 {
-       shutting_down = SHUTDOWN_SUSPEND;
-       schedule_work(&shutdown_work);
-
+       switch_shutdown_state(SHUTDOWN_SUSPEND);
        return IRQ_HANDLED;
 }



And you are calling the above busy-wait loop from within an irq handler. 
AFAIK it runs in interrupt-context and might cause dead-lock on 
uniprocessor setups (especially if underlying process context belongs to 
suspend thread itself).


regards,
--
bvk-chaitanya

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