linux-kernel - Re: [PATCH v4 1/4] mm: reduce the rcu lock duration

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Date:   Tue, 31 May 2022 14:50:31 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Miaohe Lin <linmiaohe@...wei.com>, akpm@...ux-foundation.org,
        naoya.horiguchi@....com
Cc:     peterx@...hat.com, apopple@...dia.com, ying.huang@...el.com,
        osalvador@...e.de, mike.kravetz@...cle.com,
        songmuchun@...edance.com, hch@....de, dhowells@...hat.com,
        cl@...ux.com, linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 1/4] mm: reduce the rcu lock duration

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@...edance.com>
> Reviewed-by: Christoph Hellwig <hch@....de>
> Reviewed-by: Oscar Salvador <osalvador@...e.de>
> Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>
> Cc: Huang Ying <ying.huang@...el.com>
> Cc: David Howells <dhowells@...hat.com>
> Cc: Christoph Lameter <cl@...ux.com>


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

-- 
Thanks,

David / dhildenb