[LTP] [PATCH v4] fanotify22.c: handle multiple asynchronous error events

[Jan Kara]

On Wed 25-03-26 12:43:57, 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. uses a poll() and read() loop to wait
>    until the expected.
> 
> 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, const struct test_case *ex)
> +{
> +	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) {
> +			tst_res(TFAIL, "%s: Event [%d] missing error info",
> +					ex->name, event_num);
> +			continue;
> +		}
> +
> +		if (info->error != ex->error && (ex->error2 == 0 || info->error != ex->error2)) {
> +			tst_res(TFAIL, "%s: Event [%d] unexpected errno (%d)",
> +					ex->name, event_num, info->error);

Should we add 'continue' here similarly to the failure case above? So that
we skip over the event with invalid error code... Otherwise the test looks
correct to me.

								Honza

> +		}
> +
> +		if (!first) {
> +			first = metadata;
> +			first_info = info;
> +		}
> +		total_count += info->error_count;
> +
> +		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)
>  {
> @@ -248,19 +291,54 @@ static void check_event(char *buf, size_t len, const struct test_case *ex)
>  static void do_test(unsigned int i)
>  {
>  	const struct test_case *tcase = &testcases[i];
> -	size_t read_len;
> +	size_t read_len = 0;
> +	struct pollfd pfd;
> +	unsigned int accumulated_count = 0;
>  
>  	SAFE_FANOTIFY_MARK(fd_notify, FAN_MARK_ADD|FAN_MARK_FILESYSTEM,
>  			   FAN_FS_ERROR, AT_FDCWD, MOUNT_PATH);
>  
>  	tcase->trigger_error();
>  
> -	read_len = SAFE_READ(0, fd_notify, event_buf, BUF_SIZE);
> +	pfd.fd = fd_notify;
> +	pfd.events = POLLIN;
> +
> +	while (accumulated_count < tcase->error_count) {
> +		if (poll(&pfd, 1, 5000) <= 0) {
> +			tst_res(TFAIL, "%s: Timeout waiting for events", tcase->name);
> +			goto out;
> +		}
> +
> +		char *current_pos = event_buf + read_len;
> +		int ret = read(fd_notify, current_pos, BUF_SIZE - read_len);
> +
> +		if (ret < 0) {
> +			tst_res(TFAIL, "%s: read failed: %s", tcase->name, strerror(errno));
> +			goto out;
> +		}
> +
> +		struct fanotify_event_metadata *m =
> +			(struct fanotify_event_metadata *)current_pos;
> +		while (FAN_EVENT_OK(m, ret)) {
> +			struct fanotify_event_info_error *e = get_event_info_error(m);
> +
> +			if (e)
> +				accumulated_count += e->error_count;
> +
> +			read_len += m->event_len;
> +			m = FAN_EVENT_NEXT(m, ret);
> +		}
> +	}
> +
> +	read_len = consolidate_events(event_buf, read_len, tcase);
> +
> +	check_event(event_buf, read_len, tcase);
> +
> +out:
>  
>  	SAFE_FANOTIFY_MARK(fd_notify, FAN_MARK_REMOVE|FAN_MARK_FILESYSTEM,
>  			   FAN_FS_ERROR, AT_FDCWD, MOUNT_PATH);
>  
> -	check_event(event_buf, read_len, tcase);
>  	/* Unmount and mount the filesystem to get it out of the error state */
>  	SAFE_UMOUNT(MOUNT_PATH);
>  	SAFE_MOUNT(tst_device->dev, MOUNT_PATH, tst_device->fs_type, 0, NULL);
> -- 
> 2.52.0
> 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR