tsacct: add 64-bit btime field

As there is only a 32-bit ac_btime field in taskstat and
we should handle dates after the overflow, add a new field
with the same information but 64-bit width that can hold
a full time64_t.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>

include/uapi/linux/taskstats.h

@@ -34,7 +34,7 @@
  */
 
 
-#define TASKSTATS_VERSION	9
+#define TASKSTATS_VERSION	10
 #define TS_COMM_LEN		32	/* should be >= TASK_COMM_LEN
 					 * in linux/sched.h */
 
@@ -169,6 +169,9 @@ struct taskstats {
 	/* Delay waiting for thrashing page */
 	__u64	thrashing_count;
 	__u64	thrashing_delay_total;
+
+	/* v10: 64-bit btime to avoid overflow */
+	__u64	ac_btime64;		/* 64-bit begin time */
 };
 
 

kernel/tsacct.c

@@ -36,6 +36,7 @@ void bacct_add_tsk(struct user_namespace *user_ns,
 	/* Convert to seconds for btime (note y2106 limit) */
 	btime = ktime_get_real_seconds() - div_u64(delta, USEC_PER_SEC);
 	stats->ac_btime = clamp_t(time64_t, btime, 0, U32_MAX);
+	stats->ac_btime64 = btime;
 
 	if (thread_group_leader(tsk)) {
 		stats->ac_exitcode = tsk->exit_code;