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

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Message-ID: <20160802174003.GD11767@fieldses.org>
Date:	Tue, 2 Aug 2016 13:40:03 -0400
From:	"J. Bruce Fields" <bfields@...ldses.org>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Nikolay Borisov <kernel@...p.com>, jlayton@...chiereds.net,
	viro@...iv.linux.org.uk, 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

On Tue, Aug 02, 2016 at 11:00:39AM -0500, Eric W. Biederman wrote:
> 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.

Oh, that makes sense, thanks.

What does /proc/mounts use, out of curiosity?  The mount namespace that
/proc was originally mounted in?

--b.

> 
> 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)