ipc: shm: Make shmid_kernel timestamps y2038 safe

time_t is not y2038 safe. Replace all uses of
time_t by y2038 safe time64_t.

Similarly, replace the calls to get_seconds() with
y2038 safe ktime_get_real_seconds().
Note that this preserves fast access on 64 bit systems,
but 32 bit systems need sequence counters.

The syscall interfaces themselves are not changed as part of
the patch. They will be part of a different series.

Signed-off-by: Deepa Dinamani <[e-mail]>
Reviewed-by: Arnd Bergmann <[e-mail]>
Signed-off-by: Al Viro <[e-mail]>

include/linux/shm.h

···
 	struct file		*shm_file;
 	unsigned long		shm_nattch;
 	unsigned long		shm_segsz;
-	time_t			shm_atim;
-	time_t			shm_dtim;
-	time_t			shm_ctim;
+	time64_t		shm_atim;
+	time64_t		shm_dtim;
+	time64_t		shm_ctim;
 	pid_t			shm_cprid;
 	pid_t			shm_lprid;
 	struct user_struct	*mlock_user;

ipc/shm.c

···
 	if (IS_ERR(shp))
 		return PTR_ERR(shp);
 
-	shp->shm_atim = get_seconds();
+	shp->shm_atim = ktime_get_real_seconds();
 	shp->shm_lprid = task_tgid_vnr(current);
 	shp->shm_nattch++;
 	shm_unlock(shp);
···
 		goto done; /* no-op */
 
 	shp->shm_lprid = task_tgid_vnr(current);
-	shp->shm_dtim = get_seconds();
+	shp->shm_dtim = ktime_get_real_seconds();
 	shp->shm_nattch--;
 	if (shm_may_destroy(ns, shp))
 		shm_destroy(ns, shp);
···
 	shp->shm_cprid = task_tgid_vnr(current);
 	shp->shm_lprid = 0;
 	shp->shm_atim = shp->shm_dtim = 0;
-	shp->shm_ctim = get_seconds();
+	shp->shm_ctim = ktime_get_real_seconds();
 	shp->shm_segsz = size;
 	shp->shm_nattch = 0;
 	shp->shm_file = file;
···
 		err = ipc_update_perm(&shmid64->shm_perm, ipcp);
 		if (err)
 			goto out_unlock0;
-		shp->shm_ctim = get_seconds();
+		shp->shm_ctim = ktime_get_real_seconds();
 		break;
 	default:
 		err = -EINVAL;
···
 
 	seq_printf(s,
 		   "%10d %10d  %4o " SIZE_SPEC " %5u %5u  "
-		   "%5lu %5u %5u %5u %5u %10lu %10lu %10lu "
+		   "%5lu %5u %5u %5u %5u %10llu %10llu %10llu "
 		   SIZE_SPEC " " SIZE_SPEC "\n",
 		   shp->shm_perm.key,
 		   shp->shm_perm.id,