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

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Message-ID: <8f1ff99c80db2df5947bd7880028818e2e878fdd.camel@kernel.org>
Date:   Thu, 14 Jun 2018 06:41:18 -0400
From:   Jeff Layton <jlayton@...nel.org>
To:     Konstantin Khorenko <khorenko@...tuozzo.com>,
        Kirill Gorkunov <kgorkunov@...tuozzo.com>,
        Andrey Vagin <avagin@...tuozzo.com>,
        Benjamin Coddington <bcodding@...hat.com>,
        "J. Bruce Fields" <bfields@...ldses.org>,
        Alexander Viro <viro@...iv.linux.org.uk>
Cc:     Vasily Averin <vvs@...tuozzo.com>, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/2] fs/lock: show locks info owned by dead/invisible
 processes

On Fri, 2018-06-08 at 17:27 +0300, Konstantin Khorenko 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(-)
> 

These look fine to me. I'll plan to pick them up for v4.19 unless anyone
has objections.

Thanks!
-- 
Jeff Layton <jlayton@...nel.org>