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
[off-list ref] wrote:

On Wed, Jun 21, 2023 at 5:18 PM Jason Gerecke [off-list ref] wrote:

quoted

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...)

quoted

On Thu, Jun 8, 2023 at 2:38 PM Jason Gerecke [off-list ref] wrote:

quoted

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 <redacted>

Oof, good catch. Apologies to Peter :)

Jason

Cheers,
Benjamin

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quoted

Link: https://gitlab.freedesktop.org/libinput/libinput/-/issues/901
Fixes: 17d793f3ed53 ("HID: wacom: insert timestamp to packed Bluetooth (BT) events")
CC: stable@vger.kernel.org
Signed-off-by: Jason Gerecke <jason.gerecke@wacom.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