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

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Date:	Tue, 02 Aug 2016 11:00:39 -0500
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Nikolay Borisov <kernel@...p.com>
Cc:	jlayton@...chiereds.net, viro@...iv.linux.org.uk,
	bfields@...ldses.org, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org,
	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

Nikolay Borisov <kernel@...p.com> writes:

> 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, 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.

The locks always confuse me so I am not 100% connecting locks
to a pid namespace is appropriate.

That said if you are going to filter by pid namespace please use the pid
namespace of proc, not the pid namespace of the process reading the
file.

Different contents of files depending on who opens them is generally to
be discouraged.

Eric

> 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)