netdev - Re: [bpf-next V5 PATCH 11/15] page_pool: refurbish version of page

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Message-ID: <796ac33b-26cc-107b-debe-17b5cfceab97@gmail.com>
Date:   Fri, 23 Mar 2018 07:55:37 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Jesper Dangaard Brouer <brouer@...hat.com>,
        Eric Dumazet <eric.dumazet@...il.com>
Cc:     netdev@...r.kernel.org,
        BjörnTöpel <bjorn.topel@...el.com>,
        magnus.karlsson@...el.com, eugenia@...lanox.com,
        Jason Wang <jasowang@...hat.com>,
        John Fastabend <john.fastabend@...il.com>,
        Eran Ben Elisha <eranbe@...lanox.com>,
        Saeed Mahameed <saeedm@...lanox.com>, galp@...lanox.com,
        Daniel Borkmann <borkmann@...earbox.net>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Tariq Toukan <tariqt@...lanox.com>
Subject: Re: [bpf-next V5 PATCH 11/15] page_pool: refurbish version of
 page_pool code



On 03/23/2018 07:15 AM, Jesper Dangaard Brouer wrote:
> On Fri, 23 Mar 2018 06:29:55 -0700
> Eric Dumazet <eric.dumazet@...il.com> wrote:
> 
>> On 03/23/2018 05:18 AM, Jesper Dangaard Brouer wrote:
>>
>>> +
>>> +void page_pool_destroy_rcu(struct page_pool *pool)
>>> +{
>>> +	call_rcu(&pool->rcu, __page_pool_destroy_rcu);
>>> +}
>>> +EXPORT_SYMBOL(page_pool_destroy_rcu);
>>>   
>>
>>
>> Why do we need to respect one rcu grace period before destroying a page pool ?
> 
> Due to previous allocator ID patch, which can have a pointer reference
> to a page_pool, and the allocator ID lookup uses RCU.
> 

I am not convinced.  How comes a patch that is _before_ this one can have any impact ?

Normally, we put first infrastructure, then something using it.

rcu grace period before freeing huge quantitites of pages is problematic and could
be used by syzbot to OOM the host.