linux-kernel - Re: [PATCH V2 09/10] x86/resctrl: Pseudo-lock portions of multiple resources

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Message-ID: <cdfbc993-6e73-5045-518f-51be2172675d@intel.com>
Date:   Fri, 9 Aug 2019 09:20:14 -0700
From:   Reinette Chatre <reinette.chatre@...el.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     tglx@...utronix.de, fenghua.yu@...el.com, tony.luck@...el.com,
        kuo-lang.tseng@...el.com, mingo@...hat.com, hpa@...or.com,
        x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH V2 09/10] x86/resctrl: Pseudo-lock portions of multiple
 resources

Hi Borislav,

On 8/9/2019 12:38 AM, Borislav Petkov wrote:
> On Thu, Aug 08, 2019 at 01:13:46PM -0700, Reinette Chatre wrote:
>> There is a locking order dependency between cpu_hotplug_lock and
>> rdtgroup_mutex (cpu_hotplug_lock before rdtgroup_mutex) that has to be
>> maintained. To do so in this flow you will find cpus_read_lock() in
>> rdtgroup_schemata_write(), so quite a distance from where it is needed.
>>
>> Perhaps I should add a comment at the location where the lock is
>> required to document where the lock is obtained?
> 
> Even better - you can add:
> 
> 	lockdep_assert_cpus_held();
> 
> above it which documents *and* checks too. :-)
> 

Will do.

Thank you

Reinette