Summary:

create hfs file system, loop-back mount it, run filename stressor with
stress-ng to exercise filename create/stat/unlink and we get unexpected -EEXIST errors.
This can be worked around by adding a sync() call after the unlink() to ensure
metadata is sync'd.

Kernel: 6.8.0-11-generic

test case:
sudo apt-get install hfsprogs

dd if=/dev/zero of=fs.img bs=1M count=2048
mkfs.hfs fs.img
sudo mount fs.img /mnt
sudo mkdir /mnt/x
sudo stress-ng --temp-path /mnt/x --filename 8 --filename-opts posix -t 20
stress-ng: info: [132412] setting to a 20 secs run per stressor
stress-ng: info: [132412] dispatching hogs: 8 filename
stress-ng: fail: [132424] filename: open failed on file of length 1 bytes, errno=17 (File exists)
stress-ng: fail: [132428] filename: open failed on file of length 20 bytes, errno=17 (File exists)
stress-ng: fail: [132423] filename: open failed on file of length 30 bytes, errno=17 (File exists)
stress-ng: fail: [132421] filename: open failed on file of length 30 bytes, errno=17 (File exists)
stress-ng: fail: [132428] filename: open failed on file of length 30 bytes, errno=17 (File exists)
stress-ng: fail: [132426] filename: open failed on file of length 23 bytes, errno=17 (File exists)
stress-ng: fail: [132425] filename: open failed on file of length 30 bytes, errno=17 (File exists)
stress-ng: fail: [132428] filename: open failed on file of length 1 bytes, errno=17 (File exists)
stress-ng: fail: [132423] filename: open failed on file of length 7 bytes, errno=17 (File exists)
stress-ng: fail: [132423] filename: open failed on file of length 11 bytes, errno=17 (File exists)
stress-ng: fail: [132426] filename: open failed on file of length 24 bytes, errno=17 (File exists)

adding a sync() call in the stress-ng stressor fixes the issue:

git diff
diff --git a/stress-filename.c b/stress-filename.c
index a64898fb1..b8266f91e 100644
--- a/stress-filename.c
+++ b/stress-filename.c
@@ -308,6 +308,7 @@ static void stress_filename_test(
                VOID_RET(int, shim_stat(filename, &buf));

                (void)shim_unlink(filename);
+ (void)sync();
        }

        /* exercise dcache lookup of non-existent filename */

sudo stress-ng --temp-path /mnt/x --filename 8 --filename-opts posix -t 20
stress-ng: info: [132461] setting to a 20 secs run per stressor
stress-ng: info: [132461] dispatching hogs: 8 filename
stress-ng: info: [132461] skipped: 0
stress-ng: info: [132461] passed: 8: filename (8)
stress-ng: info: [132461] failed: 0
stress-ng: info: [132461] metrics untrustworthy: 0
stress-ng: info: [132461] successful run completed in 20.05 secs

The sync should not be required by the way, I just added it to illustrate that there is a racy metadata sync issue in hfs.