fanotify_mark FAN_MARK_FLUSH | _MOUNT stress blocks write to directory

[Xiong Zhou]

hi,

This happens on 4.13.0-rc7+ to commit 42ff72c

After firing up the stress, touch a file in monitoring directory could
hang like forever.

Pretty easy to hit.

Thanks,
Xiong

[  492.060879] INFO: task touch:2259 blocked for more than 120 seconds.
[  492.093497]       Not tainted 4.13.0-rc7-master-42ff72c+ #9
[  492.121049] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[  492.156289] touch           D    0  2259   2233 0x00000080
[  492.180880] Call Trace:
[  492.191813]  __schedule+0x28d/0x890
[  492.207440]  schedule+0x36/0x80
[  492.221529]  fanotify_handle_event+0x2a1/0x2f0
[  492.241542]  ? remove_wait_queue+0x60/0x60
[  492.260150]  fsnotify+0x2d3/0x4f0
[  492.275055]  ? security_inode_init_security+0xd2/0x190
[  492.298097]  security_file_open+0x89/0x90
[  492.316038]  do_dentry_open+0x139/0x330
[  492.333216]  vfs_open+0x4f/0x70
[  492.347225]  ? may_open+0x5a/0x100
[  492.362481]  path_openat+0x548/0x13b0
[  492.378958]  do_filp_open+0x91/0x100
[  492.394969]  ? __alloc_fd+0x46/0x170
[  492.410930]  do_sys_open+0x124/0x210
[  492.426927]  SyS_open+0x1e/0x20
[  492.440963]  do_syscall_64+0x67/0x150
[  492.457367]  entry_SYSCALL64_slow_path+0x25/0x25
[  492.478251] RIP: 0033:0x7fe877f8e5a0
[  492.495755] RSP: 002b:00007ffe57120318 EFLAGS: 00000246 ORIG_RAX: 0000000000000002
[  492.529911] RAX: ffffffffffffffda RBX: 00007ffe57120578 RCX: 00007fe877f8e5a0
[  492.561508] RDX: 00000000000001b6 RSI: 0000000000000941 RDI: 00007ffe5712268c
[  492.595577] RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
[  492.631144] R10: 00007ffe57120030 R11: 0000000000000246 R12: 00007ffe5712268c
[  492.664970] R13: 00007fe8782612a0 R14: 0000000000000001 R15: 0000000000000000


--------------------------------
$ cat test.sh

#!/bin/bash -x

fallocate -l 2G test.img
mkfs.xfs -fq test.img
mkdir -p testdir
mount -o loop test.img testdir || exit

SCRATCH_MNT=$(readlink -f testdir)

function clean ()
{
	while ps -eo comm | grep -q -e fanotify ; do
		killall fanotify_flush_stress
	done

	umount -d $SCRATCH_MNT
	rm -rf test.img scrc $SCRATCH_MNT fanotify_flush_stress
}

trap "clean; exit;" 2

cc fanotify_flush_stress.c -o fanotify_flush_stress

./fanotify_flush_stress $SCRATCH_MNT &
./fanotify_flush_stress $SCRATCH_MNT &
./fanotify_flush_stress $SCRATCH_MNT &

ps jf | grep fanotify

touch $SCRATCH_MNT/1  # hang

clean

--------------------------------
$ cat fanotify_flush_stress.c

#define _GNU_SOURCE     /* Needed to get O_LARGEFILE definition */
#include <errno.h>
#include <fcntl.h>
#include <limits.h>
#include <poll.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/fanotify.h>
#include <unistd.h>
#include <string.h>

int main(int argc, char *argv[])
{
	char buf;
	int fd;

	/* Check mount point is supplied */
	if (argc != 2) {
		fprintf(stderr, "Usage: %s MOUNT\n", argv[0]);
		exit(EXIT_FAILURE);
	}

	printf("%s on %s\n", argv[0], argv[1]);
	/* Create the file descriptor for accessing the fanotify API */
	fd = fanotify_init(FAN_CLOEXEC | FAN_CLASS_CONTENT | FAN_NONBLOCK,
					   O_RDWR | O_LARGEFILE);
	if (fd == -1) {
		perror("fanotify_init");
		exit(EXIT_FAILURE);
	}

	/* Loop marking all kinds of events and flush */
	while (1) {

#if 1
		if (fanotify_mark(fd, FAN_MARK_ADD | FAN_MARK_MOUNT,
			  FAN_ACCESS | FAN_MODIFY | FAN_OPEN_PERM | FAN_CLOSE |
			  FAN_OPEN | FAN_ACCESS_PERM | FAN_ONDIR |
			  FAN_EVENT_ON_CHILD, -1, argv[1]) == -1)

			perror("fanotify_mark add");

		if (fanotify_mark(fd, FAN_MARK_FLUSH | FAN_MARK_MOUNT,
						0, -1, argv[1]) == -1)
			perror("fanotify_mark flush mount");
#else
		if (fanotify_mark(fd, FAN_MARK_ADD | FAN_MARK_MOUNT,
			  FAN_ACCESS | FAN_MODIFY | FAN_OPEN_PERM | FAN_CLOSE |
			  FAN_OPEN | FAN_ACCESS_PERM | FAN_ONDIR |
			  FAN_EVENT_ON_CHILD, -1, argv[1]) == -1)

			perror("fanotify_mark add");

		if (fanotify_mark(fd, FAN_MARK_FLUSH, 0, -1, argv[1]) == -1)
			perror("fanotify_mark flush");
#endif
	}

	close(fd);
	exit(EXIT_SUCCESS);
}