linux-kernel - Re: [RESEND PATCH v13 3/3] selftests/rseq: Add test for mm

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Message-ID: <20562227-7116-4842-b5ea-f950b615719c@efficios.com>
Date: Fri, 20 Jun 2025 13:29:14 -0400
From: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To: Gabriele Monaco <gmonaco@...hat.com>,
 Shuah Khan <skhan@...uxfoundation.org>
Cc: linux-kernel@...r.kernel.org, Peter Zijlstra <peterz@...radead.org>,
 "Paul E. McKenney" <paulmck@...nel.org>, Shuah Khan <shuah@...nel.org>,
 linux-kselftest@...r.kernel.org, Ingo Molnar <mingo@...hat.org>
Subject: Re: [RESEND PATCH v13 3/3] selftests/rseq: Add test for mm_cid
 compaction

On 2025-06-20 13:20, Gabriele Monaco wrote:
> 2025-06-18T21:04:30Z Shuah Khan <skhan@...uxfoundation.org>:
> 
>> On 6/13/25 03:12, Gabriele Monaco wrote:
>>> A task in the kernel (task_mm_cid_work) runs somewhat periodically to
>>> compact the mm_cid for each process. Add a test to validate that it runs
>>> correctly and timely.
>>> The test spawns 1 thread pinned to each CPU, then each thread, including
>>> the main one, runs in short bursts for some time. During this period, the
>>> mm_cids should be spanning all numbers between 0 and nproc.
>>> At the end of this phase, a thread with high enough mm_cid (>= nproc/2)
>>> is selected to be the new leader, all other threads terminate.
>>> After some time, the only running thread should see 0 as mm_cid, if that
>>> doesn't happen, the compaction mechanism didn't work and the test fails.
>>> The test never fails if only 1 core is available, in which case, we
>>> cannot test anything as the only available mm_cid is 0.
>>> Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
>>> Signed-off-by: Gabriele Monaco <gmonaco@...hat.com>
>>
>> Mathieu,
>>
>> Let me know if you would like me to take this through my tree.
>>
>> Acked-by: Shuah Khan <skhan@...uxfoundation.org>
> 
> Thanks for the Ack, just to add some context: the test is flaky without the previous patches, would it still be alright to pull it before them?

We need Peter Zijlstra to act on merging the fix.

Peter ?

Thanks,

Mathieu

> 
> Thanks,
> Gabriele
> 


-- 
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com