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Date:   Tue, 31 May 2022 14:50:31 +0200
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Subject: Re: [PATCH v4 1/4] mm: reduce the rcu lock duration
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To:     Miaohe Lin <linmiaohe@huawei.com>, akpm@linux-foundation.org,
        naoya.horiguchi@nec.com
Cc:     peterx@redhat.com, apopple@nvidia.com, ying.huang@intel.com,
        osalvador@suse.de, mike.kravetz@oracle.com,
        songmuchun@bytedance.com, hch@lst.de, dhowells@redhat.com,
        cl@linux.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org
References: <20220530113016.16663-1-linmiaohe@huawei.com>
 <20220530113016.16663-2-linmiaohe@huawei.com>
From:   David Hildenbrand <david@redhat.com>
Organization: Red Hat
In-Reply-To: <20220530113016.16663-2-linmiaohe@huawei.com>
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On 30.05.22 13:30, Miaohe Lin wrote:
> Commit 3268c63eded4 ("mm: fix move/migrate_pages() race on task struct")
> extends the period of the rcu_read_lock until after the permissions checks
> are done to prevent the task pointed to from changing from under us. But
> the task_struct refcount is also taken at that time, the reference to task
> is guaranteed to be stable. So it's unnecessary to extend the period of
> the rcu_read_lock. Release the rcu lock after task refcount is successfully
> grabbed to reduce the rcu holding time.
> 
> Reviewed-by: Muchun Song <songmuchun@bytedance.com>
> Reviewed-by: Christoph Hellwig <hch@lst.de>
> Reviewed-by: Oscar Salvador <osalvador@suse.de>
> Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
> Cc: Huang Ying <ying.huang@intel.com>
> Cc: David Howells <dhowells@redhat.com>
> Cc: Christoph Lameter <cl@linux.com>


Reviewed-by: David Hildenbrand <david@redhat.com>

-- 
Thanks,

David / dhildenb