linux-kernel - Re: [PATCH v4] x86/split_lock: fix delayed detection enabling

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Message-ID: <52d96674-8abd-f374-3f8a-5fe28cc82157@igalia.com>
Date: Wed, 18 Dec 2024 19:20:03 -0300
From: "Guilherme G. Piccoli" <gpiccoli@...lia.com>
To: Maksim Davydov <davydov-max@...dex-team.ru>, x86@...nel.org
Cc: den-plotnikov@...dex-team.ru, mingo@...hat.com, bp@...en8.de,
 linux-kernel@...r.kernel.org, dave.hansen@...ux.intel.com,
 tglx@...utronix.de, hpa@...or.com
Subject: Re: [PATCH v4] x86/split_lock: fix delayed detection enabling

On 17/12/2024 11:54, Maksim Davydov wrote:
> Hi!
> Ping
> 
> On 11/26/24 01:11, Maksim Davydov wrote:
>> If the warn mode with disabled mitigation mode is used, then on each
>> CPU where the split lock occurred detection will be disabled in order to
>> make progress and delayed work will be scheduled, which then will enable
>> detection back. Now it turns out that all CPUs use one global delayed
>> work structure. This leads to the fact that if a split lock occurs on
>> several CPUs at the same time (within 2 jiffies), only one CPU will
>> schedule delayed work, but the rest will not. The return value of
>> schedule_delayed_work_on() would have shown this, but it is not checked
>> in the code.
>>
>> A diagram that can help to understand the bug reproduction:
>> https://lore.kernel.org/all/2cd54041-253b-4e78-b8ea-dbe9b884ff9b@yandex-team.ru/
>>
>> In order to fix the warn mode with disabled mitigation mode, delayed work
>> has to be a per-CPU.
>>
>> v4 -> v3:
>> * rebased the patch onto the latest master
>>
>> v3 -> v2:
>> * place and time of the per-CPU structure initialization were changed.
>>    initcall doesn't seem to be a good place for it, so deferred
>>    initialization is used.
>>
>> Fixes: 727209376f49 ("x86/split_lock: Add sysctl to control the misery mode")
>> Signed-off-by: Maksim Davydov <davydov-max@...dex-team.ru>
>> ---

Hi Maksim, I've just tested this patch on top of v6.13-rc3, in a laptop
with Intel CPU that has the split lock detection - I have a quick test
case for that. Everything works fine, so feel free to add my:

Tested-by: Guilherme G. Piccoli <gpiccoli@...lia.com>

Dave / others, anything else we need to get this fix merged?
I'd be glad to help in other tests, etc.

Cheers,

Guilherme