Re: fanotify_mark FAN_MARK_FLUSH | _MOUNT stress blocks write to directory

[Amir Goldstein]

On Thu, Aug 31, 2017 at 6:51 AM, Xiong Zhou <xzhou@xxxxxxxxxx> wrote:
> hi,
>
> This happens on 4.13.0-rc7+ to commit 42ff72c

Don't understand. Is this a regression? from which commit?

>
> After firing up the stress, touch a file in monitoring directory could
> hang like forever.
>
> Pretty easy to hit.

So are running 3 processes that constantly ask to be notified
blocking on file system events and then they never read those
events. Even tough the marks are also destroyed, odd are that
at least one mark will be alive at any given time.

Why is it surprising that touching a file in monitored directory
hangs forever?

I am very happy to see someone is writing stress tests for
fanotify, I am just not sure this test is tuned correctly.
Have you been trying to reproduce a reported bug?

Amir.

>
> 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);
> }