linux-kernel - Re: [PATCH v2] HID: wacom: Use ktime_t rather than int when dealing with timestamps

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Message-ID: <CANRwn3SwEOZWxkCAU8FvFZyLHNpq78bZQtN7tbGTQjU=sQ9iAA@mail.gmail.com>
Date:   Wed, 21 Jun 2023 13:52:10 -0700
From:   Jason Gerecke <killertofu@...il.com>
To:     Benjamin Tissoires <benjamin.tissoires@...hat.com>
Cc:     linux-input@...r.kernel.org, linux-kernel@...r.kernel.org,
        Jiri Kosina <jikos@...nel.org>,
        Ping Cheng <pinglinux@...il.com>,
        Aaron Armstrong Skomra <skomra@...il.com>,
        Joshua Dickens <Joshua@...hua-dickens.com>,
        Peter Hutterer <peter.hutterer@...-t.net>,
        Jason Gerecke <jason.gerecke@...om.com>, stable@...r.kernel.org
Subject: Re: [PATCH v2] HID: wacom: Use ktime_t rather than int when dealing
 with timestamps

On Wed, Jun 21, 2023 at 9:04 AM Benjamin Tissoires
<benjamin.tissoires@...hat.com> wrote:
>
> On Wed, Jun 21, 2023 at 5:18 PM Jason Gerecke <killertofu@...il.com> wrote:
> >
> > Following up since no action seems to have been taken on this patch yet.
>
> Sorry, this went through the cracks (I seem to have a lot of cracks recently...)
>
> >
> > On Thu, Jun 8, 2023 at 2:38 PM Jason Gerecke <killertofu@...il.com> wrote:
> > >
> > > Code which interacts with timestamps needs to use the ktime_t type
> > > returned by functions like ktime_get. The int type does not offer
> > > enough space to store these values, and attempting to use it is a
> > > recipe for problems. In this particular case, overflows would occur
> > > when calculating/storing timestamps leading to incorrect values being
> > > reported to userspace. In some cases these bad timestamps cause input
> > > handling in userspace to appear hung.
>
> I have to ask, is this something we should consider writing a test for? :)
>

Very good point! I'm happy to work on such a test.

Are you open to merging this patch without delay while I write a
testcase? I don't like the idea of this (apparent) system freeze being
affecting users any longer than absolutely necessary.

> Also, you are missing the rev-by from Peter, not sure if the tools
> will pick it up automatically then.
>
> Reviewed-by: Benjamin Tissoires <benjamin.tissoires@...hat.com>
>

Oof, good catch. Apologies to Peter :)

Jason

> Cheers,
> Benjamin
>
> > >
> > > Link: https://gitlab.freedesktop.org/libinput/libinput/-/issues/901
> > > Fixes: 17d793f3ed53 ("HID: wacom: insert timestamp to packed Bluetooth (BT) events")
> > > CC: stable@...r.kernel.org
> > > Signed-off-by: Jason Gerecke <jason.gerecke@...om.com>
> > > ---
> > > v2: Use div_u64 to perform division to deal with ARC and ARM architectures
> > >     (as found by the kernel test robot)
> > >
> > >  drivers/hid/wacom_wac.c | 6 +++---
> > >  drivers/hid/wacom_wac.h | 2 +-
> > >  2 files changed, 4 insertions(+), 4 deletions(-)
> > >
> > > diff --git a/drivers/hid/wacom_wac.c b/drivers/hid/wacom_wac.c
> > > index 2ccf838371343..174bf03908d7c 100644
> > > --- a/drivers/hid/wacom_wac.c
> > > +++ b/drivers/hid/wacom_wac.c
> > > @@ -1314,7 +1314,7 @@ static void wacom_intuos_pro2_bt_pen(struct wacom_wac *wacom)
> > >         struct input_dev *pen_input = wacom->pen_input;
> > >         unsigned char *data = wacom->data;
> > >         int number_of_valid_frames = 0;
> > > -       int time_interval = 15000000;
> > > +       ktime_t time_interval = 15000000;
> > >         ktime_t time_packet_received = ktime_get();
> > >         int i;
> > >
> > > @@ -1348,7 +1348,7 @@ static void wacom_intuos_pro2_bt_pen(struct wacom_wac *wacom)
> > >         if (number_of_valid_frames) {
> > >                 if (wacom->hid_data.time_delayed)
> > >                         time_interval = ktime_get() - wacom->hid_data.time_delayed;
> > > -               time_interval /= number_of_valid_frames;
> > > +               time_interval = div_u64(time_interval, number_of_valid_frames);
> > >                 wacom->hid_data.time_delayed = time_packet_received;
> > >         }
> > >
> > > @@ -1359,7 +1359,7 @@ static void wacom_intuos_pro2_bt_pen(struct wacom_wac *wacom)
> > >                 bool range = frame[0] & 0x20;
> > >                 bool invert = frame[0] & 0x10;
> > >                 int frames_number_reversed = number_of_valid_frames - i - 1;
> > > -               int event_timestamp = time_packet_received - frames_number_reversed * time_interval;
> > > +               ktime_t event_timestamp = time_packet_received - frames_number_reversed * time_interval;
> > >
> > >                 if (!valid)
> > >                         continue;
> > > diff --git a/drivers/hid/wacom_wac.h b/drivers/hid/wacom_wac.h
> > > index 1a40bb8c5810c..ee21bb260f22f 100644
> > > --- a/drivers/hid/wacom_wac.h
> > > +++ b/drivers/hid/wacom_wac.h
> > > @@ -324,7 +324,7 @@ struct hid_data {
> > >         int ps_connected;
> > >         bool pad_input_event_flag;
> > >         unsigned short sequence_number;
> > > -       int time_delayed;
> > > +       ktime_t time_delayed;
> > >  };
> > >
> > >  struct wacom_remote_data {
> > > --
> > > 2.41.0
> > >
> >
>