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From:   Kyle Tso <kyletso@google.com>
Date:   Fri, 23 Jun 2023 18:11:00 +0800
Message-ID: <CAGZ6i=1uD-baR+Tht4+D1oC7O04K4L-RDBdDLSo6gZhNqN=2rg@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
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On Fri, Jun 23, 2023 at 6:06=E2=80=AFPM Kyle Tso <kyletso@google.com> wrote=
:
>
> On Fri, Jun 23, 2023 at 3:51=E2=80=AFPM Greg KH <gregkh@linuxfoundation.o=
rg> 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 BTYP=
E=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

BTW, to print the buf address, it should use %pK ...

Kyle