linux-kernel - [PATCH] usb: cdc-acm: fix cooldown mechanism

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Message-Id: <20201019170702.150534-1-jbrunet@baylibre.com>
Date:   Mon, 19 Oct 2020 19:07:02 +0200
From:   Jerome Brunet <jbrunet@...libre.com>
To:     Oliver Neukum <oneukum@...e.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Jerome Brunet <jbrunet@...libre.com>,
        Kevin Hilman <khilman@...libre.com>,
        linux-amlogic@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-usb@...r.kernel.org,
        Pascal Vizeli <pascal.vizeli@...ucasa.com>
Subject: [PATCH] usb: cdc-acm: fix cooldown mechanism

Commit a4e7279cd1d1 ("cdc-acm: introduce a cool down") is causing
regression if there is some USB error, such as -EPROTO.

This has been reported on some samples of the Odroid-N2 using the Combee II
Zibgee USB dongle.

> struct acm *acm = container_of(work, struct acm, work)

is incorrect in case of a delayed work and causes warnings, usually from
the workqueue:

> WARNING: CPU: 0 PID: 0 at kernel/workqueue.c:1474 __queue_work+0x480/0x528.

When this happens, USB eventually stops working completely after a while.
Also the ACM_ERROR_DELAY bit is never set, so the cooldown mechanism
previously introduced cannot be triggered and acm_submit_read_urb() is
never called.

This changes makes the cdc-acm driver use a single delayed work, fixing the
pointer arithmetic in acm_softint() and set the ACM_ERROR_DELAY when the
cooldown mechanism appear to be needed.

Fixes: a4e7279cd1d1 ("cdc-acm: introduce a cool down")
Reported-by: Pascal Vizeli <pascal.vizeli@...ucasa.com>
Cc: Oliver Neukum <oneukum@...e.com>
Signed-off-by: Jerome Brunet <jbrunet@...libre.com>
---

 Hi,

 I tried to fix problem introduced by
 commit a4e7279cd1d1 ("cdc-acm: introduce a cool down") while keeping the
 original intent, or at least what I understand of it.

 A plain revert of the original commit also works for me.

 drivers/usb/class/cdc-acm.c | 12 +++++-------
 drivers/usb/class/cdc-acm.h |  3 +--
 2 files changed, 6 insertions(+), 9 deletions(-)

diff --git a/drivers/usb/class/cdc-acm.c b/drivers/usb/class/cdc-acm.c
index f1a9043bdfe5..172cd2d21914 100644
--- a/drivers/usb/class/cdc-acm.c
+++ b/drivers/usb/class/cdc-acm.c
@@ -507,6 +507,7 @@ static void acm_read_bulk_callback(struct urb *urb)
 			"%s - cooling babbling device\n", __func__);
 		usb_mark_last_busy(acm->dev);
 		set_bit(rb->index, &acm->urbs_in_error_delay);
+		set_bit(ACM_ERROR_DELAY, &acm->flags);
 		cooldown = true;
 		break;
 	default:
@@ -532,7 +533,7 @@ static void acm_read_bulk_callback(struct urb *urb)
 
 	if (stopped || stalled || cooldown) {
 		if (stalled)
-			schedule_work(&acm->work);
+			schedule_delayed_work(&acm->dwork, 0);
 		else if (cooldown)
 			schedule_delayed_work(&acm->dwork, HZ / 2);
 		return;
@@ -562,13 +563,13 @@ static void acm_write_bulk(struct urb *urb)
 	acm_write_done(acm, wb);
 	spin_unlock_irqrestore(&acm->write_lock, flags);
 	set_bit(EVENT_TTY_WAKEUP, &acm->flags);
-	schedule_work(&acm->work);
+	schedule_delayed_work(&acm->dwork, 0);
 }
 
 static void acm_softint(struct work_struct *work)
 {
 	int i;
-	struct acm *acm = container_of(work, struct acm, work);
+	struct acm *acm = container_of(work, struct acm, dwork.work);
 
 	if (test_bit(EVENT_RX_STALL, &acm->flags)) {
 		smp_mb(); /* against acm_suspend() */
@@ -584,7 +585,7 @@ static void acm_softint(struct work_struct *work)
 	if (test_and_clear_bit(ACM_ERROR_DELAY, &acm->flags)) {
 		for (i = 0; i < acm->rx_buflimit; i++)
 			if (test_and_clear_bit(i, &acm->urbs_in_error_delay))
-					acm_submit_read_urb(acm, i, GFP_NOIO);
+				acm_submit_read_urb(acm, i, GFP_KERNEL);
 	}
 
 	if (test_and_clear_bit(EVENT_TTY_WAKEUP, &acm->flags))
@@ -1352,7 +1353,6 @@ static int acm_probe(struct usb_interface *intf,
 	acm->ctrlsize = ctrlsize;
 	acm->readsize = readsize;
 	acm->rx_buflimit = num_rx_buf;
-	INIT_WORK(&acm->work, acm_softint);
 	INIT_DELAYED_WORK(&acm->dwork, acm_softint);
 	init_waitqueue_head(&acm->wioctl);
 	spin_lock_init(&acm->write_lock);
@@ -1562,7 +1562,6 @@ static void acm_disconnect(struct usb_interface *intf)
 	}
 
 	acm_kill_urbs(acm);
-	cancel_work_sync(&acm->work);
 	cancel_delayed_work_sync(&acm->dwork);
 
 	tty_unregister_device(acm_tty_driver, acm->minor);
@@ -1605,7 +1604,6 @@ static int acm_suspend(struct usb_interface *intf, pm_message_t message)
 		return 0;
 
 	acm_kill_urbs(acm);
-	cancel_work_sync(&acm->work);
 	cancel_delayed_work_sync(&acm->dwork);
 	acm->urbs_in_error_delay = 0;
 
diff --git a/drivers/usb/class/cdc-acm.h b/drivers/usb/class/cdc-acm.h
index cd5e9d8ab237..b95ff769072e 100644
--- a/drivers/usb/class/cdc-acm.h
+++ b/drivers/usb/class/cdc-acm.h
@@ -112,8 +112,7 @@ struct acm {
 #		define ACM_ERROR_DELAY	3
 	unsigned long urbs_in_error_delay;		/* these need to be restarted after a delay */
 	struct usb_cdc_line_coding line;		/* bits, stop, parity */
-	struct work_struct work;			/* work queue entry for various purposes*/
-	struct delayed_work dwork;			/* for cool downs needed in error recovery */
+	struct delayed_work dwork;		        /* work queue entry for various purposes */
 	unsigned int ctrlin;				/* input control lines (DCD, DSR, RI, break, overruns) */
 	unsigned int ctrlout;				/* output control lines (DTR, RTS) */
 	struct async_icount iocount;			/* counters for control line changes */
-- 
2.25.4