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

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Date:   Mon, 30 Apr 2018 17:49:34 +0000
From:   "Weiny, Ira" <ira.weiny@...el.com>
To:     Doug Ledford <dledford@...hat.com>, Jason Gunthorpe <jgg@...pe.ca>,
        jackm <jackm@....mellanox.co.il>
CC:     Håkon Bugge <haakon.bugge@...cle.com>,
        "Hiatt, Don" <don.hiatt@...el.com>,
        Dasaratharaman Chandramouli 
        <dasaratharaman.chandramouli@...el.com>,
        "Hefty, Sean" <sean.hefty@...el.com>,
        OFED mailing list <linux-rdma@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] IB/core: Make ib_mad_client_id atomic

Looks fine to me.

> -----Original Message-----
> From: Doug Ledford [mailto:dledford@...hat.com]
> Sent: Monday, April 30, 2018 10:11 AM
> To: Jason Gunthorpe <jgg@...pe.ca>; jackm <jackm@....mellanox.co.il>
> Cc: Håkon Bugge <haakon.bugge@...cle.com>; Hiatt, Don
> <don.hiatt@...el.com>; Dasaratharaman Chandramouli
> <dasaratharaman.chandramouli@...el.com>; Weiny, Ira <ira.weiny@...el.com>;
> Hefty, Sean <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 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>
> 
> 
> --
> Doug Ledford <dledford@...hat.com>
>     GPG KeyID: B826A3330E572FDD
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