Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
MIME-Version: 1.0
References: <20230622150423.3726894-1-kyletso@google.com> <20230622150423.3726894-4-kyletso@google.com>
 <2023062345-hassle-septic-b8b4@gregkh>
In-Reply-To: <2023062345-hassle-septic-b8b4@gregkh>
From:   Kyle Tso <kyletso@google.com>
Date:   Fri, 23 Jun 2023 18:06:10 +0800
Message-ID: <CAGZ6i=3BP4ssx31roJoGL_VT=o3mq9Lj_VfZ_HSywzPOEt3v7g@mail.gmail.com>
Subject: Re: [PATCH 3/3] usb: typec: Use sysfs_emit_at when concatenating the string
To:     Greg KH <gregkh@linuxfoundation.org>
Cc:     heikki.krogerus@linux.intel.com, badhri@google.com,
        linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
Precedence: bulk

On Fri, Jun 23, 2023 at 3:51=E2=80=AFPM Greg KH <gregkh@linuxfoundation.org=
> wrote:
>
> On Thu, Jun 22, 2023 at 11:04:23PM +0800, Kyle Tso wrote:
> > The buffer address used in sysfs_emit should be aligned to PAGE_SIZE.
>
> Why?  Are you getting warnings about this?
>
> thanks,
>
> greg k-h

Yes, here is the warning.

[  223.243123] invalid sysfs_emit: buf:00000000eda2d647
[  223.243197] WARNING: CPU: 4 PID: 8860 at fs/sysfs/file.c:735
sysfs_emit+0xb0/0xc0
[  223.244335] CPU: 4 PID: 8860 Comm: cat
[  223.244363] pstate: 62400005 (nZCv daif +PAN -UAO +TCO -DIT -SSBS BTYPE=
=3D--)
[  223.244378] pc : sysfs_emit+0xb0/0xc0
[  223.244394] lr : sysfs_emit+0xac/0xc0
...
[  223.244560] Call trace:
[  223.244568] sysfs_emit+0xb0/0xc0
[  223.244582] select_usb_power_delivery_show+0x134/0x18c
[  223.244626] dev_attr_show+0x38/0x74
[  223.244654] sysfs_kf_seq_show+0xb4/0x130
[  223.244668] kernfs_seq_show+0x44/0x54
[  223.244683] seq_read_iter+0x158/0x4ec
[  223.244727] kernfs_fop_read_iter+0x68/0x1b0
[  223.244739] vfs_read+0x1d8/0x2b0
[  223.244775] ksys_read+0x78/0xe8

The warning comes from
https://elixir.bootlin.com/linux/v6.3.9/source/fs/sysfs/file.c#L734

if (WARN(!buf || offset_in_page(buf), "invalid sysfs_emit: buf:%p\n", buf))
        return 0;

Kyle