[SCSI] aacraid: Fix for arrays are going offline in the system. System hangs

One of the customer had reported that the set of raid logical arrays will
become unavailable (I/O offline) after a long hours of IO stress test.  The OS
wouldn`t be accessible afterwards and require a hard reset.

This driver patch has a fix for race condition between the doorbell and the
circular buffer. The driver is modified to do an extra read after clearing the
doorbell in case there had been a completion posted during the small timing
window.

With this fix, we ran IO stress for ~13 days. There were no IO failures.
Signed-off-by: NMahesh Rajashekhara <Mahesh.Rajashekhara@pmcs.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: NJames Bottomley <JBottomley@Parallels.com>

drivers/scsi/aacraid/src.c

@@ -93,6 +93,9 @@ static irqreturn_t aac_src_intr_message(int irq, void *dev_id)
 			int send_it = 0;
 			extern int aac_sync_mode;
 
+			src_writel(dev, MUnit.ODR_C, bellbits);
+			src_readl(dev, MUnit.ODR_C);
+
 			if (!aac_sync_mode) {
 				src_writel(dev, MUnit.ODR_C, bellbits);
 				src_readl(dev, MUnit.ODR_C);