Re: File system corruption after writing to unlinked file and using fdatasync on the file if system crashes

[Viacheslav Dubeyko <slava@dubeyko.com>]

On Wed, 2026-03-11 at 16:01 +0300, Vyacheslav Kovalevsky wrote:
> Detailed description
> ====================
> 
> Hello, there seems to be an issue with NILFS2 crash behavior:
> 
> 1. Create new file and truncate to some length.
> 2. Unlink the file but keep the file descriptor open.
> 3. Make new empty directory.
> 4. Sync file system.
> 5. Write some data to the file.
> 6. Apply fdatasync() to the file.
> 
> After system crash (e.g. power failure) mounting file system results
> in 
> error message `Stale file handle`. See details below.
> 
> 
> System info
> ===========
> 
> Linux version 7.0-rc2, also tested on 6.19.2
> nilfs-tools version 2.2.11
> 
> 
> How to reproduce
> ================
> 
> ```
> #include <errno.h>
> #include <fcntl.h>
> #include <stdio.h>
> #include <string.h>
> #include <sys/stat.h>
> #include <sys/types.h>
> #include <unistd.h>
> 
> int main() {
>    int status;
>    int file_fd;
> 
>    status =
>        open("file", O_WRONLY | O_CREAT, S_IRWXU | S_IRWXG | S_IROTH |
> S_IXOTH);
>    printf("OPEN: %d\n", status);
>    file_fd = status;
> 
>    status = ftruncate(file_fd, 1000);
>    printf("FTRUNCATE: %d\n", status);
> 
>    status = unlink("file");
>    printf("UNLINK: %d\n", status);
> 
>    status = mkdir("dir", S_IRWXU | S_IRWXG | S_IROTH | S_IXOTH);
>    printf("MKDIR: %d\n", status);
> 
>    sync();
> 
>    status = write(file_fd, "Test data!", 10);
>    printf("WRITE: %d\n", status);
> 
>    status = fdatasync(file_fd); // everything is fine if using
> fsync() 
> instead...
>    printf("FDATASYNC: %d\n", status);
> }
> // file system is unmountable after crash
> 
> // `mount` output:
> // mount.nilfs2: Error while mounting /dev/vdb on /mnt/fstest: Stale 
> file handle
> 
> // `dmesg` output:
> // [   29.941736] NILFS (vdb): mounting unchecked fs
> // [   29.953605] NILFS (vdb): error -116 recovering data block
> (ino=11, 
> block-offset=0)
> // [   29.953609] NILFS (vdb): error -116 roll-forwarding partial 
> segment at blocknr = 26
> ```
> 
> Steps:
> 
> 1. Create and mount new NILFS2 file system in default configuration.
> 2. Change directory to root of the file system and run the compiled
> test.
> 3. Cause hard system crash (e.g. QEMU `system_reset` command).
> 4. Remount file system after crash.
> 5. Observe that mount fails.

Thank you for the report. The issue [1] has been created.

What's about to fix the issue? ;)

Thanks,
Slava.

[1] https://github.com/nilfs-dev/nilfs2/issues/164