Re: [PATCH 0/2] fs/lock: show locks info owned by dead/invisible processes

[Murphy Zhou]

Hi,

Looks like this missed v4.18 ?

Thanks,
Murphy

On Fri, Jun 8, 2018 at 10:27 PM, Konstantin Khorenko
<khorenko@xxxxxxxxxxxxx> wrote:
> The behavior has been changed after 9d5b86ac13c5 ("fs/locks: Remove fl_nspid
> and use fs-specific l_pid for remote locks")
> and now /proc/$PID/fdinfo/$FD does not show the info about the lock
> * if the flock owner process is dead and its pid has been already freed
> or
> * if the lock owner is not visible in current pidns.
>
> CRIU uses this interface to store locks info during dump and thus can break
> on v4.13 and newer.
>
> So let's show info about locks anyway in described cases (like it was before
> 9d5b86ac13c5), but show pid number saved in file_lock struct if we are in
> init_pid_ns (patch 1) or just zero otherwise (patch 2) like we do with SID.
>
> Reproducer:
> process A       process A1      process A2
> fork()--------->
> exit()          open()
>                 flock()
>                 fork()--------->
>                 exit()          sleep()
>
> Before the patch:
> ================
> (root@vz7)/: cat /proc/${PID_A2}/fdinfo/3
> pos:    4
> flags:  02100002
> mnt_id: 257
> lock:   (root@vz7)/:
>
> After the patch:
> ===============
> (root@vz7)/:cat /proc/${PID_A2}/fdinfo/3
> pos:    4
> flags:  02100002
> mnt_id: 295
> lock:   1: FLOCK  ADVISORY  WRITE ${PID_A1} b6:f8a61:529946 0 EOF
>
> ===============
> # cat flock1.c
>
> #include <stdio.h>
> #include <stdlib.h>
> #include <unistd.h>
> #include <sys/types.h>
> #include <sys/stat.h>
> #include <sys/file.h>
> #include <fcntl.h>
>
> int main(void)
> {
>         int fd;
>         int err;
>         pid_t child_pid;
>
>         child_pid = fork();
>         if (child_pid == -1)
>                 perror("fork failed");
>         if (child_pid) {
>                 exit(0);
>         }
>
>         fd = open("/tmp/a", O_CREAT | O_RDWR);
>         if (fd == -1)
>                 perror("Failed to open the file");
>
>         err = flock(fd, LOCK_EX);
>         if (err == -1)
>                 perror("flock failed");
>
>         child_pid = fork();
>         if (child_pid == -1)
>                 perror("fork failed");
>         if (child_pid)
>                 exit(0);
>
>         sleep(10000);
>
>         return 0;
> }
>
> Konstantin Khorenko (2):
>   fs/lock: skip lock owner pid translation in case we are in init_pid_ns
>   fs/lock: show locks taken by processes from another pidns
>
>  fs/locks.c | 15 ++++++++++-----
>  1 file changed, 10 insertions(+), 5 deletions(-)
>
> --
> 2.15.1
>