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

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Message-ID: <20190809073807.GC2152@zn.tnic>
Date:   Fri, 9 Aug 2019 09:38:07 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Reinette Chatre <reinette.chatre@...el.com>
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

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. :-)

-- 
Regards/Gruss,
    Boris.

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