Re: [PATCH v2] generic: regression test for refluxfs fixes

[Zorro Lang <zlang@kernel.org>]

On Fri, Aug 21, 2026 at 04:51:55PM -0700, Darrick J. Wong wrote:
> From: Darrick J. Wong <djwong@kernel.org>
> 
> Regression test for refluxfs as found by Qualys.
> 
> Reported-by: qsa@qualys.com
> Co-developed-by: qsa@qualys.com
> Signed-off-by: "Darrick J. Wong" <djwong@kernel.org>
> ---
> v2: add co-author credits
> ---

Hi Darrick,

I just gave this patch a try on linux v7.2+ which contains the commit
2f4acd0fcd862e, but the test still fails as shown below on both xfs
and btrfs. Did I miss anything?

root@bogon:~/git/linux# git tag --contains 2f4acd0fcd862e
v7.2
v7.2-rc4
v7.2-rc5
v7.2-rc6
v7.2-rc7

root@bogon:~/git/xfstests-dev# ./check generic/1956
FSTYP         -- xfs (debug)
PLATFORM      -- Linux/x86_64 bogon 7.2.0-mainline+ #3 SMP PREEMPT_DYNAMIC Mon Aug 24 20:34:26 CST 2026
MKFS_OPTIONS  -- -f /dev/sdc1
MOUNT_OPTIONS -- -o context=system_u:object_r:root_t:s0 /dev/sdc1 /mnt/scratch

generic/1956       - output mismatch (see /root/git/xfstests-dev/results//generic/1956.out.bad)
    --- tests/generic/1956.out  2026-08-24 14:19:18.790104900 +0800
    +++ /root/git/xfstests-dev/results//generic/1956.out.bad    2026-08-24 21:41:51.884222239 +0800
    @@ -1,2 +1,2 @@
     QA output created by 1956
    -corruption not observed
    +unknown outcome 126
    ...
    (Run 'diff -u /root/git/xfstests-dev/tests/generic/1956.out /root/git/xfstests-dev/results//generic/1956.out.bad'  to see the entire diff)

HINT: You _MAY_ be missing kernel fix:
      2f4acd0fcd862e xfs: resample the data fork mapping after cycling ILOCK

Ran: generic/1956
Failures: generic/1956
Failed 1 of 1 tests

root@bogon:~/git/xfstests-dev# ./check generic/1956
FSTYP         -- btrfs
PLATFORM      -- Linux/x86_64 bogon 7.2.0-mainline+ #3 SMP PREEMPT_DYNAMIC Mon Aug 24 20:34:26 CST 2026
MKFS_OPTIONS  -- /dev/sdc1
MOUNT_OPTIONS -- -o context=system_u:object_r:root_t:s0 /dev/sdc1 /mnt/scratch

generic/1956       - output mismatch (see /root/git/xfstests-dev/results//generic/1956.out.bad)
    --- tests/generic/1956.out  2026-08-24 14:19:18.790104900 +0800
    +++ /root/git/xfstests-dev/results//generic/1956.out.bad    2026-08-24 21:44:35.654443414 +0800
    @@ -1,2 +1,2 @@
     QA output created by 1956
    -corruption not observed
    +unknown outcome 126
    ...
    (Run 'diff -u /root/git/xfstests-dev/tests/generic/1956.out /root/git/xfstests-dev/results//generic/1956.out.bad'  to see the entire diff)
Ran: generic/1956
Failures: generic/1956
Failed 1 of 1 tests


>  .gitignore             |    1 
>  src/Makefile           |    2 
>  src/refluxfs.c         |  461 ++++++++++++++++++++++++++++++++++++++++++++++++
>  tests/generic/1956     |   58 ++++++
>  tests/generic/1956.out |    2 
>  5 files changed, 523 insertions(+), 1 deletion(-)
>  create mode 100644 src/refluxfs.c
>  create mode 100755 tests/generic/1956
>  create mode 100644 tests/generic/1956.out
>

[snip]

> +#ifndef FICLONE
> +#define FICLONE _IOW(0x94, 9, int)
> +#endif
> +#ifndef XFS_SUPER_MAGIC
> +#define XFS_SUPER_MAGIC 0x58465342
> +#endif
> +
> +#define BLK 4096

This's a hard code, what if the fs blocksize or pagesize isn't 4096?

> +
> +/* ---- configuration (overridable via CLI) --------------------------------- */
> +static const char *target_path   = "/etc/passwd";
> +static const char *clone_dir     = "/var/tmp";
> +static int         nr_writers    = 32;
> +static int         nr_pressure   = 8;
> +static int         budget_s      = 300;
> +

[snip]

> +
> +#if 0
> +static int is_xfs(const char *p)
> +{
> +    struct statfs s;
> +    if (statfs(p, &s)) return -1;
> +    return s.f_type == XFS_SUPER_MAGIC;
> +}
> +#endif

If this's useless, how about remove them?

> +
> +/* FIEMAP: is the target's first extent already shared (refcount > 1)?
> + * If so the race can never see refcount==1. */
> +static int target_first_extent_shared(void)
> +{

[snip]

> +#if 0
> +    /* 2. target on XFS */
> +    int x = is_xfs(target_path);
> +    if (x < 0) die(1, "statfs target", NULL);
> +    if (!x) {
> +        BAD("target is not on XFS (f_type != XFS_SUPER_MAGIC).");
> +        INFO("RefluXFS only affects XFS with reflink=1 (mkfs.xfs default since");
> +        INFO("xfsprogs 5.1.0; backported by Red Hat for RHEL 8 GA).  Default root");
> +        INFO("fs on RHEL/CentOS/Rocky/Alma/OL/CloudLinux 8+, Fedora Server 31+,");
> +        INFO("Amazon Linux 2023.");
> +        exit(1);
> +    }
> +    OK("target is on XFS");
> +#endif

Same

> +
> +    /* 3. clone_dir on the same superblock */
> +    if (access(clone_dir, W_OK)) die(1, "clone dir not writable",
> +        "Need a writable directory on the SAME XFS filesystem as the target.");

[snip]

> +static void *pressure(void *arg)
> +{
> +    char p[600];
> +    snprintf(p, sizeof p, "%s/press.%d", workdir, (int)(intptr_t)arg);
> +    int fd = open(p, O_RDWR|O_CREAT|O_TRUNC, 0600);
> +    if (fd < 0) return NULL;
> +    char b = 0;
> +    while (!atomic_load(&stop)) {
> +        /* return values irrelevant -- goal is XFS log traffic, not the data */
> +        (void)!pwrite(fd, &b, 1, 0);
> +        (void)!ftruncate(fd, BLK);
> +        fdatasync(fd);
> +        (void)!ftruncate(fd, 0);

As this's a generic test case, the pressure() works for XFS CIL, does it work
for other filesystems?

Thanks,
Zorro