linux-kernel - Re: [PATCH] x86/resctrl: Fix potential lockdep warning

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Date:   Tue, 19 Nov 2019 15:44:46 +0800
From:   Xiaochen Shen <xiaochen.shen@...el.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     tglx@...utronix.de, mingo@...hat.com, hpa@...or.com,
        tony.luck@...el.com, fenghua.yu@...el.com,
        reinette.chatre@...el.com, x86@...nel.org,
        linux-kernel@...r.kernel.org, pei.p.jia@...el.com,
        Xiaochen Shen <xiaochen.shen@...el.com>
Subject: Re: [PATCH] x86/resctrl: Fix potential lockdep warning

On 11/18/2019 23:02, Borislav Petkov wrote:
> On Sun, Nov 17, 2019 at 12:13:20AM +0800, Xiaochen Shen wrote:
>> Actually this fix covers all the cases of an audit of the calling paths
>> of rdt_last_cmd_{clear,puts,printf}(), to make sure we only have the
>> lockdep_assert_held() in places where we are sure that it must be held.
> 
> That's kinda what I suggested, isn't it?
> 
> All I meant was, not to have a
> 
> 	rdtgroup_kn_lock_live()
> 
> call in the code as this function does *not* unconditionally grab the
> rdtgroup_mutex. And then call a function which unconditionally checks
> whether the mutex is held.
> 

Hi Boris,

Thank you for your good suggestion. I will try to follow up if we could 
improve the code in call sites of rdtgroup_kn_lock_live() in separate patch.

In my opinion, the potential lockdep issues in all call sites of 
rdt_last_cmd_{clear,puts,...}() have been fixed in this patch.

Thank you.

-- 
Best regards,
Xiaochen