s390/cpum_sf: Use kzalloc and minor changes

Use kzalloc() to allocate auxiliary buffer structure initialized
with all zeroes to avoid random value in trace output.

Avoid double access to SBD hardware flags.

Signed-off-by: Thomas Richter <tmricht@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>

arch/s390/kernel/perf_cpum_sf.c

@@ -1426,8 +1426,8 @@ static int aux_output_begin(struct perf_output_handle *handle,
 		idx = aux->empty_mark + 1;
 		for (i = 0; i < range_scan; i++, idx++) {
 			te = aux_sdb_trailer(aux, idx);
-			te->flags = te->flags & ~SDB_TE_BUFFER_FULL_MASK;
-			te->flags = te->flags & ~SDB_TE_ALERT_REQ_MASK;
+			te->flags &= ~(SDB_TE_BUFFER_FULL_MASK |
+				       SDB_TE_ALERT_REQ_MASK);
 			te->overflow = 0;
 		}
 		/* Save the position of empty SDBs */
@@ -1470,8 +1470,7 @@ static bool aux_set_alert(struct aux_buffer *aux, unsigned long alert_index,
 	te = aux_sdb_trailer(aux, alert_index);
 	do {
 		orig_flags = te->flags;
-		orig_overflow = te->overflow;
-		*overflow = orig_overflow;
+		*overflow = orig_overflow = te->overflow;
 		if (orig_flags & SDB_TE_BUFFER_FULL_MASK) {
 			/*
 			 * SDB is already set by hardware.
@@ -1711,7 +1710,7 @@ static void *aux_buffer_setup(struct perf_event *event, void **pages,
 	}
 
 	/* Allocate aux_buffer struct for the event */
-	aux = kmalloc(sizeof(struct aux_buffer), GFP_KERNEL);
+	aux = kzalloc(sizeof(struct aux_buffer), GFP_KERNEL);
 	if (!aux)
 		goto no_aux;
 	sfb = &aux->sfb;