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

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Message-Id: <20200914.125942.5644261129883859.davem@davemloft.net>
Date:   Mon, 14 Sep 2020 12:59:42 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     npiggin@...il.com
Cc:     linux-mm@...ck.org, linux-arch@...r.kernel.org,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        sparclinux@...r.kernel.org, aneesh.kumar@...ux.ibm.com,
        akpm@...ux-foundation.org, axboe@...nel.dk, peterz@...radead.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: 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>