linux-kernel - Re: [PATCH v3 3/3] IB/core: Obtain subnet

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Message-ID: <76766414-4D50-4E60-B3FC-1989026562D9@oracle.com>
Date:   Wed, 16 Jun 2021 11:20:01 +0000
From:   Haakon Bugge <haakon.bugge@...cle.com>
To:     Leon Romanovsky <leon@...nel.org>
CC:     Anand Khoje <anand.a.khoje@...cle.com>,
        OFED mailing list <linux-rdma@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "dledford@...hat.com" <dledford@...hat.com>,
        "jgg@...pe.ca" <jgg@...pe.ca>
Subject: Re: [PATCH v3 3/3] IB/core: Obtain subnet_prefix from cache in IB
 devices.



> On 15 Jun 2021, at 18:13, Haakon Bugge <haakon.bugge@...cle.com> wrote:
> 
> 
> 
>> On 15 Jun 2021, at 07:08, Leon Romanovsky <leon@...nel.org> wrote:
>> 
>> On Mon, Jun 14, 2021 at 04:29:09PM +0000, Haakon Bugge wrote:
>>> 
>>> 
>>>> On 14 Jun 2021, at 09:25, Leon Romanovsky <leon@...nel.org> wrote:
>>>> 
>>>> On Mon, Jun 14, 2021 at 03:32:39AM +0000, Haakon Bugge wrote:
>>>>> 
>>>>> 
>>>>>> On 9 Jun 2021, at 12:40, Leon Romanovsky <leon@...nel.org> wrote:
>>>>>> 
>>>>>> On Wed, Jun 09, 2021 at 09:26:03AM +0000, Anand Khoje wrote:
>>>>>>> Hi Leon,
>>>>>> 
>>>>>> Please don't do top-posting.
>>>>>> 
>>>>>> 
>>>>>>> 
>>>>>>> The set_bit()/clear_bit() and enum ib_port_data_flags  has been added as a device that can be used for future enhancements. 
>>>>>>> Also, usage of set_bit()/clear_bit() ensures the operations on this bit is atomic.
>>>>>> 
>>>>>> The bitfield variables are better suit this use case.
>>>>>> Let's don't overcomplicate code without the reason.
>>>>> 
>>>>> The problem is always that people tend to build on what's in there. For example, look at the bitfields in rdma_id_private, tos_set,  timeout_set, and min_rnr_timer_set.
>>>>> 
>>>>> What do you think will happen when, let's say, rdma_set_service_type() and rdma_set_ack_timeout() are called in close proximity in time? There is no locking, and the RMW will fail intermittently.
>>>> 
>>>> We are talking about device initialization flow that shouldn't be
>>>> performed in parallel to another initialization of same device, so the
>>>> comparison to rdma-cm is not valid here.
>>> 
>>> I can agree to that. And it is probably not worthwhile to fix the bit-fields in rdma_id_private?
>> 
>> Before this article [1], I would say no, we don't need to fix.
>> Now, I'm not sure about that.
>> 
>> "He also notes that even though the design flaws are difficult to exploit
>> on their own, they can be combined with the other flaws found to make for
>> a much more serious problem."
>> 
>> and 
>> 
>> "In other words, people did notice this vulnerability and a defense was standardized,
>> but in practice the defense was never adopted. This is a good example that security
>> defenses must be adopted before attacks become practical."
> 
> Let me send you a commit tomorrow. The last sentence you quoted above is ambiguous as far as I can understand. But the intention is clear though :-)

Do you prefer for-next or for-rc for this?

Thxs, Håkon