Re: [PATCH] serialize suspend-resume process

[BVK Chaitanya <bayapuneni_chaitanya@symantec.com>]

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