Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Thu, 18 Oct 2018 17:19:53 +0200
From:   Olaf Hering <olaf@aepfle.de>
To:     Stephen Hemminger <stephen@networkplumber.org>
Cc:     kys@microsoft.com, linux-kernel@vger.kernel.org,
        devel@linuxdriverproject.org
Subject: Re: [PATCH V2 3/4] vmbus: add per-channel sysfs info
Message-ID: <20181018171953.079f6fb6.olaf@aepfle.de>
In-Reply-To: <20170918035419.11062-3-kys@exchange.microsoft.com>
References: <20170918034955.10913-1-kys@exchange.microsoft.com>
        <20170918035419.11062-1-kys@exchange.microsoft.com>
        <20170918035419.11062-3-kys@exchange.microsoft.com>
MIME-Version: 1.0
Content-Type: multipart/signed; micalg=pgp-sha1;
 boundary="Sig_/XM3s3d1I7SWbaUwNiYVsnLE"; protocol="application/pgp-signature"
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

--Sig_/XM3s3d1I7SWbaUwNiYVsnLE
Content-Type: text/plain; charset=US-ASCII
Content-Transfer-Encoding: quoted-printable

Am Sun, 17 Sep 2017 20:54:18 -0700
schrieb kys@exchange.microsoft.com:

> This extends existing vmbus related sysfs structure to provide per-channel
> state information. This is useful when diagnosing issues with multiple
> queues in networking and storage.

> +++ b/drivers/hv/vmbus_drv.c
> +static ssize_t write_avail_show(const struct vmbus_channel *channel, cha=
r *buf)
> +{
> +	const struct hv_ring_buffer_info *rbi =3D &channel->outbound;
> +
> +	return sprintf(buf, "%u\n", hv_get_bytes_to_write(rbi));
> +}
> +VMBUS_CHAN_ATTR_RO(write_avail);

This is upstream since a year.

But I wonder how this can work if vmbus_device_register is called,
and then something reads the populated sysfs files before vmbus_open return=
s.
Nothing protects rbi->ring_buffer in this case, which remains NULL
until vmbus_open populates it.

A simple reproduce, with a modular kernel, is to boot with init=3D/bin/bash
head /sys/bus/vmbus/devices/*/channels/*/*

Olaf

--Sig_/XM3s3d1I7SWbaUwNiYVsnLE
Content-Type: application/pgp-signature
Content-Description: Digitale Signatur von OpenPGP

-----BEGIN PGP SIGNATURE-----

iF0EARECAB0WIQSkRyP6Rn//f03pRUBdQqD6ppg2fgUCW8ikmQAKCRBdQqD6ppg2
fs/+AJ96XIzUhnDlu6M7bWwTIgZ/evTZXwCfXbXPxjVEp5/d/MYiNKPXtiNrN/o=
=Ip93
-----END PGP SIGNATURE-----

--Sig_/XM3s3d1I7SWbaUwNiYVsnLE--