linux-kernel - Re: [RFC PATCH] locks: Show only file_locks created in the same pidns as current process

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Date:	Tue, 2 Aug 2016 11:05:21 -0400
From:	"J. Bruce Fields" <bfields@...ldses.org>
To:	Nikolay Borisov <kernel@...p.com>
Cc:	jlayton@...chiereds.net, viro@...iv.linux.org.uk,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	ebiederm@...ssion.com, containers@...ts.linux-foundation.org,
	serge.hallyn@...onical.com
Subject: Re: [RFC PATCH] locks: Show only file_locks created in the same
 pidns as current process

On Tue, Aug 02, 2016 at 05:42:23PM +0300, Nikolay Borisov wrote:
> Currently when /proc/locks is read it will show all the file locks
> which are currently created on the machine. On containers, hosted
> on busy servers this means that doing lsof can be very slow. I
> observed up to 5 seconds stalls reading 50k locks,

Do you mean just that the reading process itself was blocked, or that
others were getting stuck on blocked_lock_lock?

(And what process was actually reading /proc/locks, out of curiosity?)

> while the container
> itself had only a small number of relevant entries. Fix it by
> filtering the locks listed by the pidns of the current process
> and the process which created the lock.

Thanks, that's interesting.  So you show a lock if it was created by
someone in the current pid namespace.  With a special exception for the
init namespace so that 

If a filesystem is shared between containers that means you won't
necessarily be able to figure out from within a container which lock is
conflicting with your lock.  (I don't know if that's really a problem.
I'm unfortunately short on evidence aobut what people actually use
/proc/locks for....)

--b.

> 
> Signed-off-by: Nikolay Borisov <kernel@...p.com>
> ---
>  fs/locks.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/fs/locks.c b/fs/locks.c
> index 6333263b7bc8..53e96df4c583 100644
> --- a/fs/locks.c
> +++ b/fs/locks.c
> @@ -2615,9 +2615,17 @@ static int locks_show(struct seq_file *f, void *v)
>  {
>  	struct locks_iterator *iter = f->private;
>  	struct file_lock *fl, *bfl;
> +	struct pid_namespace *pid_ns = task_active_pid_ns(current);
> +
>  
>  	fl = hlist_entry(v, struct file_lock, fl_link);
>  
> +	pr_info ("Current pid_ns: %p init_pid_ns: %p, fl->fl_nspid: %p nspidof:%p\n", pid_ns, &init_pid_ns,
> +		 fl->fl_nspid, ns_of_pid(fl->fl_nspid));
> +	if ((pid_ns != &init_pid_ns) && fl->fl_nspid &&
> +		(pid_ns != ns_of_pid(fl->fl_nspid)))
> +		    return 0;
> +
>  	lock_get_status(f, fl, iter->li_pos, "");
>  
>  	list_for_each_entry(bfl, &fl->fl_block, fl_block)
> -- 
> 2.5.0