linux-kernel - Re: [PATCH 1/2] fs/lock: skip lock owner pid translation in case we are in init_pid

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Date:   Mon, 11 Jun 2018 21:35:24 -0700
From:   Andrey Vagin <avagin@...nvz.org>
To:     Konstantin Khorenko <khorenko@...tuozzo.com>
Cc:     Kirill Gorkunov <kgorkunov@...tuozzo.com>,
        Benjamin Coddington <bcodding@...hat.com>,
        Jeff Layton <jlayton@...nel.org>,
        "J. Bruce Fields" <bfields@...ldses.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Vasily Averin <vvs@...tuozzo.com>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] fs/lock: skip lock owner pid translation in case we
 are in init_pid_ns

On Fri, Jun 08, 2018 at 05:27:11PM +0300, Konstantin Khorenko wrote:
> If the flock owner process is dead and its pid has been already freed,
> pid translation won't work, but we still want to show flock owner pid
> number when expecting /proc/$PID/fdinfo/$FD in init pidns.
> 
> 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
> 

Acked-by: Andrey Vagin <avagin@...nvz.org>

> 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 | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/fs/locks.c b/fs/locks.c
> index 05e211be8684..bfee5b7f2862 100644
> --- a/fs/locks.c
> +++ b/fs/locks.c
> @@ -2072,6 +2072,13 @@ static pid_t locks_translate_pid(struct file_lock *fl, struct pid_namespace *ns)
>  		return -1;
>  	if (IS_REMOTELCK(fl))
>  		return fl->fl_pid;
> +	/*
> +	 * If the flock owner process is dead and its pid has been already
> +	 * freed, the translation below won't work, but we still want to show
> +	 * flock owner pid number in init pidns.
> +	 */
> +	if (ns == &init_pid_ns)
> +		return (pid_t)fl->fl_pid;
>  
>  	rcu_read_lock();
>  	pid = find_pid_ns(fl->fl_pid, &init_pid_ns);
> -- 
> 2.15.1
>