Re: [LTP] [PATCH v2 2/5] fanotify21: Stop relying on exited child for pidfd error

[Amir Goldstein <amir73il@gmail.com>]

On Tue, Aug 25, 2026 at 12:36:09PM +0200, Petr Vorel wrote:
> Hi all,
> 
> > fanotify21 used to verify the pidfd error case by generating an event
> > from a child process and reading the event after the child had exited.
> > This is no longer a stable way to trigger a pidfd error, because newer
> > kernels can report pidfds for exited event processes.
> 
> > Read the event from a child process in a descendant PID namespace
> > instead. The reader cannot get the pidfd in the parent PID namespace
> > from fanotify, so pidfd creation will fail and the test can verify
> > FAN_NOPIDFD, or -ESRCH with FAN_REPORT_FD_ERROR.
> 
> > Signed-off-by: AnonymeMeow <anonymemeow@gmail.com>
> > Reviewed-by: Jan Kara <jack@suse.cz>
> > Reviewed-by: Amir Goldstein <amir73il@gmail.com>
> 
> ...
> >  	/*
> > -	 * Generate the event in either self or a child process. Event
> > -	 * generation in a child process is done so that the FAN_NOPIDFD case
> > -	 * can be verified.
> > +	 * Read the event in either self or a child process in a descendant
> > +	 * PID namespace. A reader in a descendant PID namespace cannot obtain
> > +	 * the pidfd of the event process in the parent PID namespace so that
> > +	 * the FAN_NOPIDFD case can be verified.
> >  	 */
> > -	if (tc->fork)
> > -		do_fork();
> > -	else
> > -		generate_event();
> > +	if (tc->want_pidfd_err && (reader_pid = SAFE_CLONE(&clone_args))) {
> nit: although I'd write it this way as well, checkpatch does not like this
> effective way :) (do not use assignment in if condition).
> 
> > +		SAFE_WAITPID(reader_pid, &reader_exit_status, 0);
> > +		if (!WIFEXITED(reader_exit_status) || WEXITSTATUS(reader_exit_status))
> > +			tst_brk(TBROK, "reader process exited incorrectly");
> 
> nit: And the above should be probably replaced with tst_reap_children().
> 
> But because I should have merged this long time ago to prevent false positive on
> 7.2, merging it now. Cleanup can be done later (together with using designated
> initializers).
> 
> Merged the rest of the patch, thank you!
> 

Hi Petr,

Sorry I did not have time to investigate and need to leave now
just wanted to let you know that test ends with failure exit code.
and does not seem to run with pretty recent rc7 kernel.

Is that expected?
Maybe it's something in my own test env.

Thanks,
Amir.

root@kvm-xfstests:~/ltp# ./fanotify/fanotify20 || echo FAIL
tst_tmpdir.c:308: TINFO: Using /tmp/LTP_fanTTAwH1 as tmpdir (tmpfs filesystem)
tst_kconfig.c:90: TINFO: Parsing kernel config '/proc/config.gz'
tst_kconfig.c:756: TINFO: CONFIG_PROVE_LOCKING kernel option detected which might slow the execution
tst_device.c:103: TINFO:[  787.367492] loop0: detected capacity change from 0 to 614400
 Found free device 0 '/dev/loop0'
tst_test.c:2048: TINFO: LTP version: 20260529-243-g9118a480c
tst_tes[  787.391529] /dev/zero: Can't lookup blockdev
t.c:2051: TINFO: Tested kernel: 7.2.0-rc7-xfstests-00008-g55d5763db1de #2982 SMP PREEMPT_DYNAMIC Thu Aug 27 12:04:04 CEST 2026 x86_64
tst_test.c:1876: TINFO: Overall timeout per run is 0h 02m 00s
tst_supported_fs_types.c:108: TINFO: Kernel supports ext2
tst_supported_fs_types.c:67: TINFO: mkfs.ext2 does exist
[  787.418143] /dev/zero: Can't lookup blockdev
tst_supported_fs_types.c:108: TINFO: Kernel supports ext3
tst_supported_fs_types.c:67: TINFO: mkfs.ext3 does exist
[  787.443657] /dev/zero: Can't lookup blockdev
tst_supported_fs_types.c:108: TINFO: Kernel supports ext4
tst_supported_fs_types.c:67: TINFO: m[  787.467489] /dev/zero: Can't lookup blockdev
kfs.ext4 does exist
tst_supported_fs_types.c:108: TINFO: Kernel supports xfs
tst_supported_fs_types.c:67: TINFO: mkfs.xfs does exist
tst_supported_fs_types.c:108: TINFO: Kernel supports btrfs
tst_supported_fs_types.c:67: TINFO: mkfs.btrfs does exist
tst_supported_fs_types.c:117: TINFO: Skipping bcachefs because of FUSE blacklist
[  787.521515] /dev/zero: Can't lookup blockdev
tst_supported_fs_types.c:108: TINFO: Kernel supports vfat
tst_supported_fs_types.c:67: TINFO: mkfs.vfat does exist
tst_supported_fs_types.c:140: TINFO: Filesystem exfat is not supported
tst_supported_fs_types.c:144: TINFO: FUSE does support ntfs
tst_supported_fs_types.c:63: TINFO: mkfs.ntfs does not exist
[  787.576420] /dev/zero: Can't lookup blockdev
tst_supported_fs_types.c:108: TINFO: Kernel supports ntfs3
tst_supported_fs_types.c:63: TINFO: mkfs.ntfs does not exist
tst_supported_fs_types.c:108: TINFO: Kernel supports tmpfs
tst_supported_fs_types.c:51: TINFO: mkfs is not needed for tmpfs
tst_test.c:1986: TINFO: === Testing on ext2 ===
fanotify20.c:51: TCONF: FAN_REPORT_PIDFD | FAN_REPORT_TID is supported since v7.2
tst_test.c:1986: TINFO: === Testing on ext3 ===
fanotify20.c:51: TCONF: FAN_REPORT_PIDFD | FAN_REPORT_TID is supported since v7.2
tst_test.c:1986: TINFO: === Testing on ext4 ===
fanotify20.c:51: TCONF: FAN_REPORT_PIDFD | FAN_REPORT_TID is supported since v7.2
tst_test.c:1986: TINFO: === Testing on xfs ===
fanotify20.c:51: TCONF: FAN_REPORT_PIDFD | FAN_REPORT_TID is supported since v7.2
tst_test.c:1986: TINFO: === Testing on btrfs ===
fanotify20.c:51: TCONF: FAN_REPORT_PIDFD | FAN_REPORT_TID is supported since v7.2
tst_test.c:1986: TINFO: === Testing on vfat ===
fanotify20.c:51: TCONF: FAN_REPORT_PIDFD | FAN_REPORT_TID is supported since v7.2
tst_test.c:1986: TINFO: === Testing on tmpfs ===
fanotify20.c:51: TCONF: FAN_REPORT_PIDFD | FAN_REPORT_TID is supported since v7.2

Summary:
passed   0
failed   0
broken   0
skipped  7
warnings 0

FAIL


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