[LTP] interesting breakage in ltp fanotify10

[Amir Goldstein]

On Mon, Jun 23, 2025 at 4:45 PM Al Viro <viro@zeniv.linux.org.uk> wrote:
>
> On Mon, Jun 23, 2025 at 09:24:22AM +0200, Amir Goldstein wrote:
> > On Sun, Jun 22, 2025 at 11:51 PM Al Viro <viro@zeniv.linux.org.uk> 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)
>
> How old is your ltp tree?  Mine was from late May (81d460ba6737 "overcommit_memory:
> Disable optimization for malloc to prevent false positives")

My LTP tree is from end of May tag 20250530

> and I'm definitely
> seeing that behaviour with fanotify23 as well.  No TWARN, though -

I have no idea where this strange TWARN is coming from
I did not investigate it, but the bug is there anyway, so I sent a fix.

Thanks,
Amir.