[PATCH #upstream-fixes] sata_mv fix MSI irq race condition

[Mark Lord <liml@rtr.ca>]

Fix a (rare) race condition in mv_interrupt() when using MSI.

The value of hpriv->main_irq_mask_addr can change on on the fly,
and without this patch we could end up writing back a stale copy
to the hardware.

Signed-off-by: Mark Lord <mlord@pobox.com>
--

** This is required for 2.6.29 and beyond ***

--- old/drivers/ata/sata_mv.c	2009-03-10 16:19:39.000000000 -0400
+++ new/drivers/ata/sata_mv.c	2009-03-10 16:21:29.000000000 -0400
@@ -2218,12 +2218,13 @@
 		else
 			handled = mv_host_intr(host, pending_irqs);
 	}
-	spin_unlock(&host->lock);
 
 	/* for MSI: unmask; interrupt cause bits will retrigger now */
 	if (using_msi)
 		writel(hpriv->main_irq_mask, hpriv->main_irq_mask_addr);
 
+	spin_unlock(&host->lock);
+
 	return IRQ_RETVAL(handled);
 }