linux-kernel - Re: [PATCH v2 4/4] mm: lock slub page when listing objects

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Message-ID: <0100016d2b224ef4-8660f7e9-3093-48fa-bc40-63d20e9f2444-000000@email.amazonses.com>
Date:   Fri, 13 Sep 2019 14:58:51 +0000
From:   Christopher Lameter <cl@...ux.com>
To:     Yu Zhao <yuzhao@...gle.com>
cc:     Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Kirill A . Shutemov" <kirill@...temov.name>,
        Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 4/4] mm: lock slub page when listing objects

On Wed, 11 Sep 2019, Yu Zhao wrote:

> Though I have no idea what the side effect of such race would be,
> apparently we want to prevent the free list from being changed
> while debugging the objects.

process_slab() is called under the list_lock which prevents any allocation
from the free list in the slab page. This means that new objects can be
added to the freelist which occurs by updating the freelist pointer in the
slab page with a pointer to the newly free object which in turn contains
the old freelist pointr.

It is therefore possible to safely traverse the objects on the freelist
after the pointer has been retrieved

NAK.