On Wed, Jan 25, 2017 at 1:48 PM, Marko Rauhamaa
<marko.rauhamaa@xxxxxxxxxxxx> wrote:
>
> We have run into an easily reproducible fanotify hang that affects
> several distros as well as the latest development kernel. (It isn't
> fixed by Amir Goldstein's recent fanotify patch, BTW.)
>
Not sure what is the role that autofs is playing in this hang, but it is worth
checking if Jan's latest work fixes the problem. I estimate that it should,
because it isolated the user space handling of permission events from
affecting processes generating fsnotify events on other fs objects.
git://git.kernel.org/pub/scm/linux/kernel/git/jack/linux-fs.git #for_testing
> Here is a simple reproduction:
>
> 1. Compile and build the tiny test program below, which has been
> adapted from the example in "man fanotify":
>
> cc -o fantest3 fantest.c
>
> 2. Install autofs.
>
> 3. Run these commands as root:
>
> mkdir -p foo/home/test foo/user/test
> echo /sshome /etc/auto.sshome >/etc/auto.master
> echo "test / :/root/foo/home/test /user :/root/foo/user/test" \
> >/etc/auto.sshome
> systemctl start autofs
> ls -l /sshome/test
> ./fantest3 / /sshome/test /sshome/test/user/
>
> # NB! The final slash in the fantest3 command can be significant!
>
> 4. Observe the last command hang. While it is hung, other file system
> operations from other processes are blocked.
You mean other processes not trying to access objects under the
watched mounts. right?
>
> 5. Press Ctrl-C to force fantest3 to exit. The file system becomes
> alive. Rerunning the fantest3 command no longer hangs.
>
> 6. To get back into the problem state, execute (as root):
>
> systemctl restart autofs
> ls -l /sshome/test
> ./fantest3 / /sshome/test /sshome/test/user/
>
>
> ===Begin fantest.c======================================================
> #include <fcntl.h>
> #include <stdio.h>
> #include <stdlib.h>
> #include <sys/fanotify.h>
>
> int main(int argc, char *argv[])
> {
> int fd, i;
> if (argc < 2) {
> fprintf(stderr, "Usage: %s MOUNT ...\n", argv[0]);
> exit(EXIT_FAILURE);
> }
> fd = fanotify_init(FAN_CLOEXEC | FAN_CLASS_CONTENT | FAN_NONBLOCK,
> O_RDONLY);
> if (fd == -1) {
> perror("fanotify_init");
> exit(EXIT_FAILURE);
> }
> for (i = 1; i < argc; i++)
> if (fanotify_mark(fd, FAN_MARK_ADD | FAN_MARK_MOUNT,
> FAN_OPEN_PERM | FAN_CLOSE_WRITE, AT_FDCWD,
> argv[i]) == -1) {
> perror("fanotify_mark");
> exit(EXIT_FAILURE);
> }
> exit(EXIT_SUCCESS);
> }
> ===End fantest.c========================================================
>
>
> Marko
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