Re: [PATCH v2] locks: Filter /proc/locks output on proc pid ns

Nikolay Borisov
2016-08-03T14:34:07Z

On 08/03/2016 05:28 PM, J. Bruce Fields wrote:
> On Wed, Aug 03, 2016 at 05:17:09PM +0300, Nikolay Borisov wrote:
>>
>>
>> On 08/03/2016 04:46 PM, Jeff Layton wrote:
>>> On Wed, 2016-08-03 at 10:35 +0300, Nikolay Borisov wrote:
>>>> On busy container servers reading /proc/locks shows all the locks
>>>> created by all clients. This can cause large latency spikes. In my
>>>> case I observed lsof taking up to 5-10 seconds while processing around
>>>> 50k locks. Fix this by limiting the locks shown only to those created
>>>> in the same pidns as the one the proc was mounted in. When reading
>>>> /proc/locks from the init_pid_ns show everything.
>>>>
>>>>> Signed-off-by: Nikolay Borisov <kernel@kyup.com>
>>>> ---
>>>> fs/locks.c | 6 ++++++
>>>> 1 file changed, 6 insertions(+)
>>>>
>>>> diff --git a/fs/locks.c b/fs/locks.c
>>>> index ee1b15f6fc13..751673d7f7fc 100644
>>>> --- a/fs/locks.c
>>>> +++ b/fs/locks.c
>>>> @@ -2648,9 +2648,15 @@ static int locks_show(struct seq_file *f, void *v)
>>>> {
>>>>> struct locks_iterator *iter = f->private;
>>>>> struct file_lock *fl, *bfl;
>>>>> + struct pid_namespace *proc_pidns = file_inode(f->file)->i_sb->s_fs_info;
>>>>> + struct pid_namespace *current_pidns = task_active_pid_ns(current);
>>>>
>>>>> fl = hlist_entry(v, struct file_lock, fl_link);
>>>>
>>>>>> + if ((current_pidns != &init_pid_ns) && fl->fl_nspid
>>>
>>> Ok, so when you read from a process that's in the init_pid_ns
>>> namespace, then you'll get the whole pile of locks, even when reading
>>> this from a filesystem that was mounted in a different pid_ns?
>>>
>>> That seems odd to me if so. Any reason not to just uniformly use the
>>> proc_pidns here?
>>
>> [CCing some people from openvz/CRIU]
>>
>> My train of thought was "we should have means which would be the one
>> universal truth about everything and this would be a process in the
>> init_pid_ns".
>
> OK, but why not make that means be "mount proc from the init_pid_ns and
> read /proc/locks there". So just replace current_pidns with proc_pidns
> in the above. I think that's all Jeff was suggesting.

Oh, you are right. Silly me, yes, I'm happy with this and I will send a
patch.

>
> --b.
>
>> I don't have strong preference as long as I'm not breaking
>> userspace. As I said before - I think the CRIU guys might be using that
>> interface.
>>
>>>
>>>>>> + && (proc_pidns != 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)
>>>