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Subject: Re: [PATCH] x86/resctrl: Ensure usage of CPUs are locked while needed
To:     Borislav Petkov <bp@alien8.de>
Cc:     tglx@linutronix.de, fenghua.yu@intel.com, tony.luck@intel.com,
        jithu.joseph@intel.com, mingo@redhat.com, hpa@zytor.com,
        x86@kernel.org, linux-kernel@vger.kernel.org,
        stable@vger.kernel.org
References: <725073a1f4448e3c45ed7102229e6946ca2526d8.1543428144.git.reinette.chatre@intel.com>
 <20181210204915.GH5482@zn.tnic>
From:   Reinette Chatre <reinette.chatre@intel.com>
Message-ID: <27626243-cc7d-d289-2ebd-de5c8cc193e2@intel.com>
Date:   Mon, 10 Dec 2018 12:51:35 -0800
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Hi Boris,

On 12/10/2018 12:49 PM, Borislav Petkov wrote:
> On Wed, Nov 28, 2018 at 10:22:07AM -0800, Reinette Chatre wrote:
>> The user triggers the creation of a pseudo-locked region when writing
>> the requested schemata to the schemata resctrl file. The pseudo-locking
>> of a region is required to be done on a CPU that is associated with the
>> cache on which the pseudo-locked region will reside. In order to run the
>> locking code on a specific CPU the needed CPU has to be selected and
>> ensured to remain online during the entire locking sequence.
>>
>> At this time the cpu_hotplug_lock is not taken during the pseudo-lock
>> region creation and it is thus possible for a CPU to be selected to run
>> the pseudo-locking code and then that CPU to go offline before the
>> thread is able to run on it.
>>
>> Fix this by ensuring that the cpu_hotplug_lock is taken while the CPU on
>> which code has to run needs to be controlled. Since the cpu_hotplug_lock
>> is always taken before rdtgroup_mutex the lock order is maintained.
>>
>> Fixes: e0bdfe8e36f3 ("x86/intel_rdt: Support creation/removal of pseudo-locked region")
>> Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
>> Cc: stable@vger.kernel.org
>> ---
>>  arch/x86/kernel/cpu/resctrl/ctrlmondata.c | 4 ++++
>>  1 file changed, 4 insertions(+)
> 
> This looks like it wants to go in now, right?

Yes, please.

> 
> If so, pls redo this patch against tip/x86/urgent which has the old
> filenames, before the resctrl rename and reorg.

Will do.

Thank you

Reinette