diff --git a/drivers/ata/libata-sff.c b/drivers/ata/libata-sff.c
index db90aa3..2e86e3b 100644
--- a/drivers/ata/libata-sff.c
+++ b/drivers/ata/libata-sff.c
@@ -1333,7 +1333,19 @@
 	DPRINTK("ENTER\n");
 
 	cancel_delayed_work_sync(&ap->sff_pio_task);
+
+	/*
+	 * We wanna reset the HSM state to IDLE.  If we do so without
+	 * grabbing the port lock, critical sections protected by it which
+	 * expect the HSM state to stay stable may get surprised.  For
+	 * example, we may set IDLE in between the time
+	 * __ata_sff_port_intr() checks for HSM_ST_IDLE and before it calls
+	 * ata_sff_hsm_move() causing ata_sff_hsm_move() to BUG().
+	 */
+	spin_lock_irq(ap->lock);
 	ap->hsm_task_state = HSM_ST_IDLE;
+	spin_unlock_irq(ap->lock);
+
 	ap->sff_pio_task_link = NULL;
 
 	if (ata_msg_ctl(ap))