libata: no special completion processing for EH commands

ata_qc_complete() contains special handling for certain commands.  For
example, it schedules EH for device revalidation after certain
configurations are changed.  These shouldn't be applied to EH
commands but they were.

In most cases, it doesn't cause an actual problem because EH doesn't
issue any command which would trigger special handling; however, ACPI
can issue such commands via _GTF which can cause weird interactions.

Restructure ata_qc_complete() such that EH commands are always passed
on to __ata_qc_complete().

stable: Please apply to -stable only after 2.6.38 is released.
Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: Kyle McMartin <kyle@mcmartin.ca>
Cc: stable@kernel.org
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>

drivers/ata/libata-core.c

@@ -4807,9 +4807,6 @@ static void ata_verify_xfer(struct ata_queued_cmd *qc)
 {
 	struct ata_device *dev = qc->dev;
 
-	if (ata_tag_internal(qc->tag))
-		return;
-
 	if (ata_is_nodata(qc->tf.protocol))
 		return;
 
@@ -4858,14 +4855,23 @@ void ata_qc_complete(struct ata_queued_cmd *qc)
 		if (unlikely(qc->err_mask))
 			qc->flags |= ATA_QCFLAG_FAILED;
 
-		if (unlikely(qc->flags & ATA_QCFLAG_FAILED)) {
-			/* always fill result TF for failed qc */
+		/*
+		 * Finish internal commands without any further processing
+		 * and always with the result TF filled.
+		 */
+		if (unlikely(ata_tag_internal(qc->tag))) {
 			fill_result_tf(qc);
+			__ata_qc_complete(qc);
+			return;
+		}
 
-			if (!ata_tag_internal(qc->tag))
+		/*
+		 * Non-internal qc has failed.  Fill the result TF and
+		 * summon EH.
+		 */
+		if (unlikely(qc->flags & ATA_QCFLAG_FAILED)) {
+			fill_result_tf(qc);
 			ata_qc_schedule_eh(qc);
-			else
-				__ata_qc_complete(qc);
 			return;
 		}