[PATCH resend 4/4] nfc: Fix hangup of RC-S380* in port100_send_ack()

From: OGAWA Hirofumi
Date: Fri Feb 03 2017 - 20:17:03 EST



If port100_send_ack() was called twice or more, it has race to hangup.

port100_send_ack() port100_send_ack()
init_completion()
[...]
dev->cmd_cancel = true
/* this removes previous from completion */
init_completion()
[...]
dev->cmd_cancel = true
wait_for_completion()
/* never be waked up */
wait_for_completion()

Like above race, this code is not assuming port100_send_ack() is
called twice or more.

To fix, this checks dev->cmd_cancel to know if prior cancel is
in-flight or not. And never be remove prior task from completion by
using reinit_completion(), so this guarantees to be waked up properly
soon or later.

Signed-off-by: OGAWA Hirofumi <hirofumi@xxxxxxxxxxxxxxxxxx>
---

drivers/nfc/port100.c | 37 ++++++++++++++++++++++++-------------
1 file changed, 24 insertions(+), 13 deletions(-)

diff -puN drivers/nfc/port100.c~nfc-port100-hang-fix drivers/nfc/port100.c
--- linux-ibmpc/drivers/nfc/port100.c~nfc-port100-hang-fix 2017-01-03 12:32:13.261785257 +0900
+++ linux-ibmpc-hirofumi/drivers/nfc/port100.c 2017-01-03 12:33:51.965364300 +0900
@@ -726,23 +726,33 @@ static int port100_submit_urb_for_ack(st

static int port100_send_ack(struct port100 *dev)
{
- int rc;
+ int rc = 0;

mutex_lock(&dev->out_urb_lock);

- init_completion(&dev->cmd_cancel_done);
-
- usb_kill_urb(dev->out_urb);
+ /*
+ * If prior cancel is in-flight (dev->cmd_cancel == true), we
+ * can skip to send cancel. Then this will wait the prior
+ * cancel, or merged into the next cancel rarely if next
+ * cancel was started before waiting done. In any case, this
+ * will be waked up soon or later.
+ */
+ if (!dev->cmd_cancel) {
+ reinit_completion(&dev->cmd_cancel_done);

- dev->out_urb->transfer_buffer = ack_frame;
- dev->out_urb->transfer_buffer_length = sizeof(ack_frame);
- rc = usb_submit_urb(dev->out_urb, GFP_KERNEL);
+ usb_kill_urb(dev->out_urb);

- /* Set the cmd_cancel flag only if the URB has been successfully
- * submitted. It will be reset by the out URB completion callback
- * port100_send_complete().
- */
- dev->cmd_cancel = !rc;
+ dev->out_urb->transfer_buffer = ack_frame;
+ dev->out_urb->transfer_buffer_length = sizeof(ack_frame);
+ rc = usb_submit_urb(dev->out_urb, GFP_KERNEL);
+
+ /*
+ * Set the cmd_cancel flag only if the URB has been
+ * successfully submitted. It will be reset by the out
+ * URB completion callback port100_send_complete().
+ */
+ dev->cmd_cancel = !rc;
+ }

mutex_unlock(&dev->out_urb_lock);

@@ -929,8 +939,8 @@ static void port100_send_complete(struct
struct port100 *dev = urb->context;

if (dev->cmd_cancel) {
+ complete_all(&dev->cmd_cancel_done);
dev->cmd_cancel = false;
- complete(&dev->cmd_cancel_done);
}

switch (urb->status) {
@@ -1546,6 +1556,7 @@ static int port100_probe(struct usb_inte
PORT100_COMM_RF_HEAD_MAX_LEN;
dev->skb_tailroom = PORT100_FRAME_TAIL_LEN;

+ init_completion(&dev->cmd_cancel_done);
INIT_WORK(&dev->cmd_complete_work, port100_wq_cmd_complete);

/* The first thing to do with the Port-100 is to set the command type
_

--
OGAWA Hirofumi <hirofumi@xxxxxxxxxxxxxxxxxx>