Dear NILFS2 Maintainers, I hope this message finds you well. I am writing to report a potential bug we have encountered in NILFS2 related to disk space management while testing it with our model checking tool, Metis. The issue arises after performing the following operations: Steps to Reproduce: 1. Mount the NILFS2 file system. 2. Continuously create files in the NILFS2 file system until the disk space is completely used up (ENOSPC). 3. Delete all the files created in the previous step. 4. Sleep for 1 minute to allow the cleanerd to run. 5. Repeat steps 2-4 a few times. Note: The protection_period parameter in nilfs_cleanerd.conf has been changed from the default 3600 seconds to 10 seconds for quicker observation of the bug. Expected Behavior: After deleting all files, the disk usage should decrease to zero or near zero, reflecting the freed space. Observed Behavior: Occasionally, after deleting the files, the file system remains stuck at a high usage (88% or 100% in our experiments) and does not free any space. When we try to create another file, it fails and reports "no space left on the device". We also tried manually running the cleanerd once the system’s space usage was stuck at high percentages; even though some of the segments appear to be not protected and have 0% live blocks, according to the lssu output, the space was still not cleaned. This issue occurs sporadically and is not consistent across all tests (thus, we suspect it may be a race condition). We have created a GitHub repository containing a detailed README, the script used to generate this problem, an example log generated in one of our experiments, and the necessary files. Running this script and obtaining all the outputs takes approximately 10 minutes. The script sets up a ramdisk and mounts NILFS2 with the minimum possible size of 1028 KiB. Here is the link to the GitHub repository: https://github.com/sbu-fsl/nilfs2-full-space.git. I would appreciate any insights or assistance you could provide regarding this issue. If you require any further information, logs, or specific test cases, please let me know, and I will be happy to provide them. Best regards, Yifei Liu File systems and Storage Lab (Stony Brook University)
