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

J. Bruce Fields
2016-08-02T15:05:51Z

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@kyup.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