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From:   "Michael Kelley (LINUX)" <mikelley@microsoft.com>
To:     Anssi Hannula <anssi.hannula@bitwise.fi>,
        KY Srinivasan <kys@microsoft.com>,
        Haiyang Zhang <haiyangz@microsoft.com>,
        Stephen Hemminger <sthemmin@microsoft.com>,
        Wei Liu <wei.liu@kernel.org>, Dexuan Cui <decui@microsoft.com>
CC:     "linux-hyperv@vger.kernel.org" <linux-hyperv@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: RE: [PATCH] hv_balloon: rate-limit "Unhandled message" warning
Thread-Topic: [PATCH] hv_balloon: rate-limit "Unhandled message" warning
Thread-Index: AQHYJ/eP+P92t79ZhEqBs3JJG71Sz6ykoZ9Q
Date:   Fri, 25 Feb 2022 18:59:18 +0000
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References: <20220222141400.98160-1-anssi.hannula@bitwise.fi>
In-Reply-To: <20220222141400.98160-1-anssi.hannula@bitwise.fi>
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From: Anssi Hannula <anssi.hannula@bitwise.fi> Sent: Tuesday, February 22, =
2022 6:14 AM
>=20
> For a couple of times I have encountered a situation where
>=20
>   hv_balloon: Unhandled message: type: 12447
>=20
> is being flooded over 1 million times per second with various values,
> filling the log and consuming cycles, making debugging difficult.
>=20
> Add rate limiting to the message.
>=20
> Most other Hyper-V drivers already have similar rate limiting in their
> message callbacks.
>=20
> The cause of the floods in my case was probably fixed by 96d9d1fa5cd5
> ("Drivers: hv: balloon: account for vmbus packet header in
> max_pkt_size").
>=20
> Fixes: 9aa8b50b2b3d ("Drivers: hv: Add Hyper-V balloon driver")
> Signed-off-by: Anssi Hannula <anssi.hannula@bitwise.fi>
> ---
>  drivers/hv/hv_balloon.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>=20
> diff --git a/drivers/hv/hv_balloon.c b/drivers/hv/hv_balloon.c
> index f2d05bff4245..439f99b8b5de 100644
> --- a/drivers/hv/hv_balloon.c
> +++ b/drivers/hv/hv_balloon.c
> @@ -1563,7 +1563,7 @@ static void balloon_onchannelcallback(void *context=
)
>                         break;
>=20
>                 default:
> -                       pr_warn("Unhandled message: type: %d\n", dm_hdr->=
type);
> +                       pr_warn_ratelimited("Unhandled message: type: %d\=
n", dm_hdr->type);
>=20
>                 }
>         }
> --
> 2.34.1

Unlike some of the other VMbus drivers, this driver has not been "hardened"=
 for
use in an environment where the guest does not trust the hypervisor, but it=
 was
affected by changes to the underlying ring buffer handling.  The bug that c=
aused
the flood of errors has indeed been fixed, but I'm good with rate limiting =
this
warning.

Reviewed-by: Michael Kelley <mikelley@microsoft.com>