linux-kernel - Re: [PATCH v2 3/4] sparc64: remove mm_cpumask clearing to fix kthread_use

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Message-Id: <20200915.124254.1657521903825160294.davem@davemloft.net>
Date:   Tue, 15 Sep 2020 12:42:54 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     npiggin@...il.com
Cc:     akpm@...ux-foundation.org, aneesh.kumar@...ux.ibm.com,
        axboe@...nel.dk, linux-arch@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linuxppc-dev@...ts.ozlabs.org, peterz@...radead.org,
        sparclinux@...r.kernel.org
Subject: Re: [PATCH v2 3/4] sparc64: remove mm_cpumask clearing to fix
 kthread_use_mm race

From: Nicholas Piggin <npiggin@...il.com>
Date: Tue, 15 Sep 2020 13:24:07 +1000

> Excerpts from David Miller's message of September 15, 2020 5:59 am:
>> From: Nicholas Piggin <npiggin@...il.com>
>> Date: Mon, 14 Sep 2020 14:52:18 +1000
>> 
>>  ...
>>> The basic fix for sparc64 is to remove its mm_cpumask clearing code. The
>>> optimisation could be effectively restored by sending IPIs to mm_cpumask
>>> members and having them remove themselves from mm_cpumask. This is more
>>> tricky so I leave it as an exercise for someone with a sparc64 SMP.
>>> powerpc has a (currently similarly broken) example.
>>> 
>>> Signed-off-by: Nicholas Piggin <npiggin@...il.com>
>> 
>> Sad to see this optimization go away, but what can I do:
>> 
>> Acked-by: David S. Miller <davem@...emloft.net>
>> 
> 
> Thanks Dave, any objection if we merge this via the powerpc tree
> to keep the commits together?

No objection.