Re: [LTP] [PATCH v2] fanotify22.c: handle multiple asynchronous error events

Jan Kara
2026-03-09T11:30:05Z

On Mon 09-03-26 07:59:42, Wei Gao wrote:
> Since the introduction of the asynchronous fserror reporting framework
> (kernel commit 81d2e13a57c9), fanotify22 has encountered sporadic failures
> due to the non-deterministic nature of event delivery and merging:
>
> 1) tcase3 failure: A race condition occurs when the test reads the
> notification fd between two events. Adding a short delay
> (usleep) ensures all events are dispatched and ready before the
> read() call.
>
> 2) tcase4 failure: The kernel may deliver errors as independent events
> instead of a single merged event, since different worker kthread can
> end up generating each event so they won't be merged. As suggested by
> Jan Kara, this patch introduces a consolidate_events() helper. It iterates
> through the event buffer, accumulates the error_count from all independent
> events, and updates the first event's count in-place.
>
> Reported-by: kernel test robot <oliver.sang@intel.com>
> Closes: https://lore.kernel.org/oe-lkp/202602042124.87bd00e3-lkp@intel.com
> Suggested-by: Jan Kara <jack@suse.cz>
> Signed-off-by: Wei Gao <wegao@suse.com>
...
> +static size_t consolidate_events(char *buf, size_t len)
> +{
> + struct fanotify_event_metadata *metadata, *first = NULL;
> + struct fanotify_event_info_error *first_info = NULL;
> + unsigned int total_count = 0;
> + int event_num = 0;
> +
> + for (metadata = (struct fanotify_event_metadata *)buf;
> + FAN_EVENT_OK(metadata, len);
> + metadata = FAN_EVENT_NEXT(metadata, len)) {
> +
> + event_num++;
> + struct fanotify_event_info_error *info = get_event_info_error(metadata);
> +
> + if (info) {
> + if (!first) {
> + first = metadata;
> + first_info = info;
> + }
> + total_count += info->error_count;

Please verify the 'error' field in the info matches before merging the
count and fail the test if it does not. Also if we get event without error
info I think we should fail the test as it currently shouldn't happen for
any of the tests.

Honza

> +
> + tst_res(TINFO, "Event [%d]: errno=%d, error_count=%d",
> + event_num, info->error, info->error_count);
> + }
> + }
> +
> + if (first_info)
> + first_info->error_count = total_count;
> +
> + return (first) ? first->event_len : 0;
> +}
> +
> static int check_error_event_info_fid(struct fanotify_event_info_fid *fid,
> const struct test_case *ex)
> {
> @@ -255,7 +286,11 @@ static void do_test(unsigned int i)
>
> tcase->trigger_error();
>
> + /* Wait for asynchronous kworker threads to dispatch events */
> + usleep(100000);
> +
> read_len = SAFE_READ(0, fd_notify, event_buf, BUF_SIZE);
> + read_len = consolidate_events(event_buf, read_len);
>
> SAFE_FANOTIFY_MARK(fd_notify, FAN_MARK_REMOVE|FAN_MARK_FILESYSTEM,
> FAN_FS_ERROR, AT_FDCWD, MOUNT_PATH);
> --
> 2.52.0
>
--
Jan Kara <jack@suse.com>
SUSE Labs, CR