Re: interesting breakage in ltp fanotify10

[Amir Goldstein <amir73il@xxxxxxxxx>]

On Sun, Jun 22, 2025 at 11:51 PM Al Viro <viro@xxxxxxxxxxxxxxxxxx> wrote:
>
>         LTP 6763a3650734 "syscalls/fanotify10: Add test cases for evictable
> ignore mark" has an interesting effect on boxen where FANOTIFY is not
> enabled.  The thing is, tst_brk() ends up calling ->cleanup().  See the
> problem?
>         SAFE_FILE_PRINTF(CACHE_PRESSURE_FILE, "%d", old_cache_pressure);
> is executed, even though
>         SAFE_FILE_SCANF(CACHE_PRESSURE_FILE, "%d", &old_cache_pressure);
>         /* Set high priority for evicting inodes */
>         SAFE_FILE_PRINTF(CACHE_PRESSURE_FILE, "500");
> hadn't been.
>
>         Result: fanotify10 on such kernel configs ends up zeroing
> /proc/sys/vm/vfs_cache_pressure.

oops.
strange enough, I cannot reproduce it as something is preventing
zeroing vfs_cache_pressure:

fanotify23.c:232: TCONF: fanotify not configured in kernel
fanotify23.c:249: TWARN: Failed to close FILE
'/proc/sys/vm/vfs_cache_pressure': EINVAL (22)

# cat /proc/sys/vm/vfs_cache_pressure
100

But I'll send a fix all the same.

Thanks,
Amir.