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Subject: Re: [PATCH] IB/core: Make ib_mad_client_id atomic
From:   =?utf-8?Q?H=C3=A5kon_Bugge?= <haakon.bugge@oracle.com>
In-Reply-To: <1524856116.11756.85.camel@redhat.com>
Date:   Mon, 30 Apr 2018 13:50:57 +0200
Cc:     jackm <jackm@dev.mellanox.co.il>, Jason Gunthorpe <jgg@ziepe.ca>,
        Don Hiatt <don.hiatt@intel.com>,
        Ira Weiny <ira.weiny@intel.com>,
        Sean Hefty <sean.hefty@intel.com>,
        OFED mailing list <linux-rdma@vger.kernel.org>,
        linux-kernel@vger.kernel.org
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To:     Doug Ledford <dledford@redhat.com>
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> On 27 Apr 2018, at 21:08, Doug Ledford <dledford@redhat.com> wrote:
>=20
> On Thu, 2018-04-26 at 20:51 +0200, H=C3=A5kon Bugge wrote:
>>> Jason is out this week.  I'll end up processing this one (probably =
later
>>> today).  But I=E2=80=99ll fix up the commit message to suit my =
tastes when I do.
>>=20
>> Thank you, Doug and Jack,
>=20
> I reworded the commit message, let me know if you think I worded it
> wrong:
>=20
> commit 69f01b81539c62f3dd96f9f02138ad7b839a0c70 (HEAD -> =
k.o/wip/dl-for-rc)
> Author: H=C3=A5kon Bugge <haakon.bugge@oracle.com>
> Date:   Wed Apr 18 16:24:50 2018 +0200
>=20
>    IB/core: Make ib_mad_client_id atomic
>=20
>    Currently, 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: "Then =
initiating
>    a new operation, MADHeader:TransactionID shall be set to such a =
value
>    that within that MAD the combination of TIG, SGID, and MgmtClass is
>    different from that of any other currently executing operation. If =
the
>    MAD does not have a GRH, its SLID is used in the combination in =
place of
>    an SGID." which guarantees we are legal because our different ports =
will
>    have different SGID/SLID creating a unique tuple even if the TIDs =
are
>    identical), and as we might want to open the TID allocator up to =
more
>    parallel usage later, make the TID an atomic type so that no two
>    allocations, regardless of port number, will be the same.

The wording is OK per se, but the last sentence spans 12 lines - and as =
such - a little bit hard to comprehend. I suggest just to refer to IB =
Spec 1.3, clause C13-18.1.1 and not quote it and make the last =
sub-sentence (starting with =E2=80=9Cand as we might want to open=E2=80=9D=
) a sentence by its own.


Thxs, H=C3=A5kon

>=20
>    Signed-off-by: H=C3=A5kon Bugge <haakon.bugge@oracle.com>
>    Reviewed-by: Jack Morgenstein <jackm@dev.mellanox.co.il>
>    Reviewed-by: Ira Weiny <ira.weiny@intel.com>
>    Reviewed-by: Zhu Yanjun <yanjun.zhu@oracle.com>
>    Signed-off-by: Doug Ledford <dledford@redhat.com>
>=20
> --=20
> Doug Ledford <dledford@redhat.com>
>    GPG KeyID: B826A3330E572FDD
>    Key fingerprint =3D AE6B 1BDA 122B 23B4 265B  1274 B826 A333 0E57 =
2FDD