linux-kernel - Re: [PATCH] IB/core: Make ib_mad_client

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Message-Id: <451F533C-60E1-4154-9540-92CB83276446@oracle.com>
Date:   Tue, 1 May 2018 08:40:07 +0200
From:   Håkon Bugge <haakon.bugge@...cle.com>
To:     jackm <jackm@....mellanox.co.il>
Cc:     Doug Ledford <dledford@...hat.com>, Jason Gunthorpe <jgg@...pe.ca>,
        Don Hiatt <don.hiatt@...el.com>,
        Dasaratharaman Chandramouli 
        <dasaratharaman.chandramouli@...el.com>,
        Ira Weiny <ira.weiny@...el.com>,
        Sean Hefty <sean.hefty@...el.com>,
        OFED mailing list <linux-rdma@...r.kernel.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] IB/core: Make ib_mad_client_id atomic



> On 1 May 2018, at 06:38, jackm <jackm@....mellanox.co.il> wrote:
> 
> On Mon, 30 Apr 2018 13:10:49 -0400
> Doug Ledford <dledford@...hat.com> wrote:
> 
> Looks good!

Yes, absolutely!

Håkon

> 
> -Jack
> 
>> On Mon, 2018-04-30 at 08:49 -0600, Jason Gunthorpe wrote:
>>> On Mon, Apr 23, 2018 at 10:16:18PM +0300, jackm wrote:
>>> 
>>>>>> TIDs need to be globally unique on the entire machine.    
>>>> Jason, that is not exactly correct.  
>>> 
>>> The expecation for /dev/umad users is that they all receive locally
>>> unique TID prefixes. The kernel may be OK to keep things
>>> port-specific but it is slightly breaking the API we are presenting
>>> to userspace to allow them to alias..
>>> 
>>> Jason  
>> 
>> Would people be happier with this commit message then:
>> 
>> IB/core: Make ib_mad_client_id atomic
>> 
>> Currently, the kernel protects access to the agent ID allocator on a
>> per port basis using a spinlock, so it is impossible for two
>> apps/threads on the same port to get the same TID, but it is entirely
>> possible for two threads on different ports to end up with the same
>> TID.  
>> 
>> As this can be confusing (regardless of it being legal according to
>> the IB Spec 1.3, C13-18.1.1, in section 13.4.6.4 - TransactionID
>> usage), and as the rdma-core user space API for /dev/umad devices
>> implies unique TIDs even across ports, make the TID an atomic type so
>> that no two allocations, regardless of port number, will be the same.
>> 
>> Signed-off-by: Håkon Bugge <haakon.bugge@...cle.com>
>> Reviewed-by: Jack Morgenstein <jackm@....mellanox.co.il>
>> Reviewed-by: Ira Weiny <ira.weiny@...el.com>
>> Reviewed-by: Zhu Yanjun <yanjun.zhu@...cle.com>
>> Signed-off-by: Doug Ledford <dledford@...hat.com>
>> 
>> 
> 
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