linux-kernel - Re: [PATCH 2/2] fs/lock: show locks taken by processes from another pidns

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Date:   Thu, 14 Jun 2018 07:00:07 -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, Nikolay Borisov <kernel@...p.com>
Subject: Re: [PATCH 2/2] fs/lock: show locks taken by processes from another
 pidns

On Fri, 2018-06-08 at 17:27 +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/$file
> 
> Let's show information about such locks again as previously, but
> show zero in the owner pid field.
> 
> After the patch:
> ===============
> (root@vz7)/:cat /proc/${PID_A2}/fdinfo/3
> pos:    4
> flags:  02100002
> mnt_id: 295
> lock:   1: FLOCK  ADVISORY  WRITE 0 b6:f8a61:529946 0 EOF
> 
> Fixes: 9d5b86ac13c5 ("fs/locks: Remove fl_nspid and use fs-specific l_pid for remote locks")
> Signed-off-by: Konstantin Khorenko <khorenko@...tuozzo.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);

(cc'ing Nickolay)

As Andrey points out, this behavior was originally added in commit
d67fd44f697d to address performance issues when there are a lot of locks
held by tasks in other namespaces.

Will allowing this code to show these again cause a problem there?
-- 
Jeff Layton <jlayton@...nel.org>