ioatdma: fix race between updating ioat->head and IOAT_COMPLETION_PENDING

There is a race that can hit during __cleanup() when the ioat->head pointer is
incremented during descriptor submission. The __cleanup() can clear the
PENDING flag when it does not see any active descriptors. This causes new
submitted descriptors to be ignored because the COMPLETION_PENDING flag is
cleared. This was introduced when code was adapted from ioatdma v1 to ioatdma
v2. For v2 and v3, IOAT_COMPLETION_PENDING flag will be abandoned and a new
flag IOAT_CHAN_ACTIVE will be utilized. This flag will also be protected under
the prep_lock when being modified in order to avoid the race.

Signed-off-by: Dave Jiang <dave.jiang@intel.com>
Reviewed-by: Dan Williams <djbw@fb.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>

drivers/dma/ioat/dma.h

@@ -97,6 +97,7 @@ struct ioat_chan_common {
 	#define IOAT_KOBJ_INIT_FAIL 3
 	#define IOAT_RESHAPE_PENDING 4
 	#define IOAT_RUN 5
+	#define IOAT_CHAN_ACTIVE 6
 	struct timer_list timer;
 	#define COMPLETION_TIMEOUT msecs_to_jiffies(100)
 	#define IDLE_TIMEOUT msecs_to_jiffies(2000)