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SubjectRe: [PATCH 2/2] fs/lock: show locks taken by processes from another pidns
On Fri, Jun 08, 2018 at 05:27:12PM +0300, Konstantin Khorenko wrote:
> Currently if we face a lock taken by a process invisible in the current
> pidns we skip the lock completely, but this
>
> 1) makes the output not that nice
> (root@vz7)/: cat /proc/${PID_A2}/fdinfo/3
> pos: 4
> flags: 02100002
> mnt_id: 257
> lock: (root@vz7)/:
>
> 2) makes it more difficult to debug issues with leaked flocks
> if you get error on lock, but don't see any locks in /proc/$id/fdinfo/$file

3) breaks the CRIU project. criu reads fdinfo to dump file locks.

>
> Let's show information about such locks again as previously, but
> show zero in the owner pid field.
>
> After the patch:
> ===============
> (root@vz7)/:cat /proc/${PID_A2}/fdinfo/3
> pos: 4
> flags: 02100002
> mnt_id: 295
> lock: 1: FLOCK ADVISORY WRITE 0 b6:f8a61:529946 0 EOF
>

I think initially this was broken in this commit:

Fixes: d67fd44f697d ("locks: Filter /proc/locks output on proc pid ns")


Acked-by: Andrei Vagin <avagin@openvz.org>

Thanks,
Andrei

> Fixes: 9d5b86ac13c5 ("fs/locks: Remove fl_nspid and use fs-specific l_pid for remote locks")
> Signed-off-by: Konstantin Khorenko <khorenko@virtuozzo.com>
> ---
> fs/locks.c | 8 +++-----
> 1 file changed, 3 insertions(+), 5 deletions(-)
>
> diff --git a/fs/locks.c b/fs/locks.c
> index bfee5b7f2862..e533623e2e99 100644
> --- a/fs/locks.c
> +++ b/fs/locks.c
> @@ -2633,12 +2633,10 @@ static void lock_get_status(struct seq_file *f, struct file_lock *fl,
>
> fl_pid = locks_translate_pid(fl, proc_pidns);
> /*
> - * If there isn't a fl_pid don't display who is waiting on
> - * the lock if we are called from locks_show, or if we are
> - * called from __show_fd_info - skip lock entirely
> + * If lock owner is dead (and pid is freed) or not visible in current
> + * pidns, zero is shown as a pid value. Check lock info from
> + * init_pid_ns to get saved lock pid value.
> */
> - if (fl_pid == 0)
> - return;
>
> if (fl->fl_file != NULL)
> inode = locks_inode(fl->fl_file);
> --
> 2.15.1
>

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