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

Wei Gao via ltp
2026-03-25T12:45:04Z

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>
---
v3->v4:
1)Fixed read_len logic by using m->event_len inside the loop to avoid overcounting.
2)Removed redundant if (info) check in consolidate_events.

.../kernel/syscalls/fanotify/fanotify22.c | 86 ++++++++++++++++++-
1 file changed, 82 insertions(+), 4 deletions(-)

diff --git a/testcases/kernel/syscalls/fanotify/fanotify22.c b/testcases/kernel/syscalls/fanotify/fanotify22.c
index e8002b160..e79213b40 100644
--- a/testcases/kernel/syscalls/fanotify/fanotify22.c
+++ b/testcases/kernel/syscalls/fanotify/fanotify22.c
@@ -28,6 +28,7 @@
#include "tst_test.h"
#include <sys/fanotify.h>
#include <sys/types.h>
+#include <poll.h>

#ifdef HAVE_SYS_FANOTIFY_H
#include "fanotify.h"
@@ -88,7 +89,6 @@ static void trigger_bad_link_lookup(void)
ret, BAD_LINK, errno, EUCLEAN);
}

-
static void tcase3_trigger(void)
{
trigger_bad_link_lookup();
@@ -104,6 +104,7 @@ static void tcase4_trigger(void)
static struct test_case {
char *name;
int error;
+ int error2;
unsigned int error_count;
struct fanotify_fid_t *fid;
void (*trigger_error)(void);
@@ -134,10 +135,52 @@ static struct test_case {
.trigger_error = &tcase4_trigger,
.error_count = 2,
.error = EFSCORRUPTED,
+ .error2 = ESHUTDOWN,
.fid = &bad_file_fid,
}
};

+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);
+ }
+
+ 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