linux-kernel - Re: [PATCH 4/4] lockdep: make MAX_LOCK

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Message-ID: <alpine.LNX.2.20.1709292301420.24635@cae-iprp-alln-lb.cisco.com>
Date:   Fri, 29 Sep 2017 23:03:04 -0700
From:   Govindarajulu Varadarajan <gvaradar@...co.com>
To:     Bjorn Helgaas <helgaas@...nel.org>
CC:     Peter Zijlstra <peterz@...radead.org>, <benve@...co.com>,
        <bhelgaas@...gle.com>, <linux-pci@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <jlbec@...lplan.org>, <hch@....de>,
        <mingo@...hat.com>
Subject: Re: [PATCH 4/4] lockdep: make MAX_LOCK_DEPTH configurable from
 Kconfig

On Fri, 29 Sep 2017, Bjorn Helgaas wrote:

> On Thu, Sep 28, 2017 at 04:51:46PM -0700, Govindarajulu Varadarajan wrote:
>> On Thu, 28 Sep 2017, Peter Zijlstra wrote:
>>
>>> On Wed, Sep 27, 2017 at 02:42:20PM -0700, Govindarajulu Varadarajan wrote:
>>>> Make MAX_LOCK_DEPTH configurable. It is set to 48 right now. Number of
>>>> VFs under a PCI pf bus can exceed 48 and this disables lockdep.
>>>>
>>>> lockdep currently allows max of 63 held_locks.
>>>
>>> But why a config knob? Why not just raise the number to 64
>>> unconditionally? And is that sufficient; you only state 48 is
>>> insufficient, you don't actually state the VF limit.
>>>
>>
>> I did not want to change the default configuration for everyone.
>>
>> I will change it 63 unconditionally in v2 and resubmit the series.
>
> I'm not happy about having to increase MAX_LOCK_DEPTH based on a
> number of VFs.  I haven't had time to look at the locking strategy
> you're proposing, but it just doesn't feel right to have to take 50+
> locks for one operation.

I agree. I have sent V2 where we dont lock 50+ device_lock. Please have a look.