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From: "Boyer, Andrew" <Andrew.Boyer@amd.com>
To: Stephen Hemminger <stephen@networkplumber.org>
CC: "Boyer, Andrew" <Andrew.Boyer@amd.com>, "dev@dpdk.org" <dev@dpdk.org>,
"Patel, Neel" <Neel.Patel@amd.com>, "stable@dpdk.org" <stable@dpdk.org>
Subject: Re: [PATCH 04/13] net/ionic: fix missing volatile type for cqe
pointers
Thread-Topic: [PATCH 04/13] net/ionic: fix missing volatile type for cqe
pointers
Thread-Index: AQHaVg6sxEkbhOyxa0qCHcOWhnGDtLD4BjsAgAO9UoA=
Date: Mon, 5 Feb 2024 13:33:11 +0000
Message-ID: <0D66E753-A5A3-4F4A-A532-1BE2FD55493D@amd.com>
References: <20240202193238.62669-1-andrew.boyer@amd.com>
<20240202193238.62669-5-andrew.boyer@amd.com>
<20240202202636.450b1b38@hermes.local>
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Errors-To: stable-bounces@dpdk.org
> On Feb 2, 2024, at 11:26 PM, Stephen Hemminger <stephen@networkplumber.or=
g> wrote:
>=20
> Caution: This message originated from an External Source. Use proper caut=
ion when opening attachments, clicking links, or responding.
>=20
>=20
> On Fri, 2 Feb 2024 11:32:29 -0800
> Andrew Boyer <andrew.boyer@amd.com> wrote:
>=20
>> From: Neel Patel <neel.patel@amd.com>
>>=20
>> This memory may be changed by the hardware, so the volatile
>> keyword is required for correctness.
>>=20
>> Fixes: e86a6fcc7cf3 ("net/ionic: add optimized non-scattered Rx/Tx")
>> cc: stable@dpdk.org
>>=20
>> Signed-off-by: Andrew Boyer <andrew.boyer@amd.com>
>> Signed-off-by: Neel Patel <neel.patel@amd.com>
>=20
> In general barriers are better than volatile.
> Volatile is a compiler not hardware construct really.
>=20
> https://www.kernel.org/doc/html/latest/process/volatile-considered-harmfu=
l.html
Thanks for looking. The goal here is to prevent inappropriate compiler opti=
mization.
>From the link you posted:
> Pointers to data structures in coherent memory which might be modified by=
I/O devices can, sometimes, legitimately be volatile. A ring buffer used b=
y a network adapter, where that adapter changes pointers to indicate which =
descriptors have been processed, is an example of this type of situation.
Doesn't that sound like what we are doing?
Thanks,
Andrew