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Date:   Fri, 4 Dec 2020 23:11:32 -0800
From:   Davidlohr Bueso <dave@stgolabs.net>
To:     Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc:     Mauro Carvalho Chehab <mchehab@kernel.org>,
        Frederic Weisbecker <frederic@kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Alan Stern <stern@rowland.harvard.edu>,
        linux-usb@vger.kernel.org
Subject: Re: [RFC PATCH] usb: hcd: complete URBs in threaded-IRQ context
 instead of tasklet
Message-ID: <20201205071132.noumprob5kgkrvyy@linux-p48b.lan>
References: <20180216170450.yl5owfphuvltstnt@breakpoint.cc>
 <20180227143934.2aa847ac@vento.lan>
 <20180308095739.okdn7ghvlpy4oiy5@linutronix.de>
 <20180416140103.33s2xarrxxeecttk@linutronix.de>
 <20201204062257.GA13304@linux-p48b.lan>
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On Thu, 03 Dec 2020, Bueso wrote:

>On Mon, 16 Apr 2018, Sebastian Andrzej Siewior wrote:
>
>>On 2018-03-08 10:57:39 [+0100], To Mauro Carvalho Chehab wrote:
>>>On 2018-02-27 14:39:34 [-0300], Mauro Carvalho Chehab wrote:
>>>> Hi Sebastian,
>>>Hi Mauro,
>>>
>>>> Sorry for taking some time to test it, has been busy those days...
>>>:)
>>>
>>>> Anyway, I tested it today. Didn't work. It keep losing data.
>>>
>>>Okay, this was unexpected. What I learned from the thread is that you
>>>use the dwc2 controller and once upgrade to a kernel which completes the
>>>URBs in BH context then you starting losing data from your DVB-s USB
>>>device. And it was assumed that this is because BH/ksoftirq is getting
>>>"paused" if it is running for too long. If that is the case then a
>>>revert of "let us complete the URB in BH context" should get it working
>>>again. Is that so?
>>
>>ping
>
>I ran into this while looking at getting rid of tasklets in drivers/usb.
>
>Mauro, were you ever able to try reverting 8add17cf8e4 like Sebastian suggested?
>If not would you mind trying the below, please? Considering this thread is from
>over two years ago, it's a rebase of Sebastian's patch to complete urbs in process
>context + the dwc2 changes not to use defer urb into bh.

Hmm Mauro's email bounced, updating with a valid address.

>
>Thanks,
>Davidlohr
>
>----8<---------------------------------------------------------------------------
>diff --git a/drivers/usb/core/hcd.c b/drivers/usb/core/hcd.c
>index 60886a7464c3..4952a8fc1719 100644
>--- a/drivers/usb/core/hcd.c
>+++ b/drivers/usb/core/hcd.c
>@@ -1665,33 +1665,76 @@ static void __usb_hcd_giveback_urb(struct urb *urb)
>	usb_put_urb(urb);
>}
>
>-static void usb_giveback_urb_bh(struct tasklet_struct *t)
>+static void usb_hcd_rh_gb_urb(struct work_struct *work)
>{
>-	struct giveback_urb_bh *bh = from_tasklet(bh, t, bh);
>-	struct list_head local_list;
>+	struct giveback_urb *bh;
>+	struct list_head urb_list;
>+
>+	bh = container_of(work, struct giveback_urb, rh_compl);
>
>	spin_lock_irq(&bh->lock);
>-	bh->running = true;
>- restart:
>-	list_replace_init(&bh->head, &local_list);
>+	list_replace_init(&bh->rh_head, &urb_list);
>	spin_unlock_irq(&bh->lock);
>
>-	while (!list_empty(&local_list)) {
>+	while (!list_empty(&urb_list)) {
>		struct urb *urb;
>
>-		urb = list_entry(local_list.next, struct urb, urb_list);
>+		urb = list_first_entry(&urb_list, struct urb, urb_list);
>		list_del_init(&urb->urb_list);
>-		bh->completing_ep = urb->ep;
>		__usb_hcd_giveback_urb(urb);
>-		bh->completing_ep = NULL;
>+	}
>+}
>+
>+#define URB_PRIO_HIGH	0
>+#define URB_PRIO_LOW	1
>+
>+static irqreturn_t usb_hcd_gb_urb(int irq, void *__hcd)
>+{
>+	struct usb_hcd *hcd = __hcd;
>+	struct giveback_urb *bh = &hcd->gb_urb;
>+	struct list_head urb_list[2];
>+	int i;
>+
>+	INIT_LIST_HEAD(&urb_list[URB_PRIO_HIGH]);
>+	INIT_LIST_HEAD(&urb_list[URB_PRIO_LOW]);
>+
>+	spin_lock_irq(&bh->lock);
>+ restart:
>+	list_splice_tail_init(&bh->prio_hi_head, &urb_list[URB_PRIO_HIGH]);
>+	list_splice_tail_init(&bh->prio_lo_head, &urb_list[URB_PRIO_LOW]);
>+	spin_unlock_irq(&bh->lock);
>+
>+	for (i = 0; i < ARRAY_SIZE(urb_list); i++) {
>+		while (!list_empty(&urb_list[i])) {
>+			struct urb *urb;
>+
>+			urb = list_first_entry(&urb_list[i],
>+					       struct urb, urb_list);
>+			list_del_init(&urb->urb_list);
>+			if (i == URB_PRIO_HIGH)
>+				bh->completing_ep = urb->ep;
>+
>+			__usb_hcd_giveback_urb(urb);
>+
>+			if (i == URB_PRIO_HIGH)
>+				bh->completing_ep = NULL;
>+
>+			if (i == URB_PRIO_LOW &&
>+			    !list_empty_careful(&urb_list[URB_PRIO_HIGH])) {
>+				spin_lock_irq(&bh->lock);
>+				goto restart;
>+			}
>+		}
>	}
>
>	/* check if there are new URBs to giveback */
>	spin_lock_irq(&bh->lock);
>-	if (!list_empty(&bh->head))
>+	if (!list_empty(&bh->prio_hi_head) ||
>+	    !list_empty(&bh->prio_lo_head))
>		goto restart;
>-	bh->running = false;
>	spin_unlock_irq(&bh->lock);
>+
>+	return IRQ_HANDLED;
>}
>
>/**
>@@ -1717,37 +1760,34 @@ static void usb_giveback_urb_bh(struct tasklet_struct *t)
> */
>void usb_hcd_giveback_urb(struct usb_hcd *hcd, struct urb *urb, int status)
>{
>-	struct giveback_urb_bh *bh;
>-	bool running, high_prio_bh;
>+	struct giveback_urb	*bh = &hcd->gb_urb;
>+	struct list_head	*lh;
>
>	/* pass status to tasklet via unlinked */
>	if (likely(!urb->unlinked))
>		urb->unlinked = status;
>
>-	if (!hcd_giveback_urb_in_bh(hcd) && !is_root_hub(urb->dev)) {
>-		__usb_hcd_giveback_urb(urb);
>+	if (is_root_hub(urb->dev)) {
>+		spin_lock(&bh->lock);
>+		list_add_tail(&urb->urb_list, &bh->rh_head);
>+		spin_unlock(&bh->lock);
>+		queue_work(system_highpri_wq, &bh->rh_compl);
>		return;
>	}
>
>-	if (usb_pipeisoc(urb->pipe) || usb_pipeint(urb->pipe)) {
>-		bh = &hcd->high_prio_bh;
>-		high_prio_bh = true;
>-	} else {
>-		bh = &hcd->low_prio_bh;
>-		high_prio_bh = false;
>+	if (!hcd_giveback_urb_in_bh(hcd)) {
>+		__usb_hcd_giveback_urb(urb);
>+		return;
>	}
>
>+	if (usb_pipeisoc(urb->pipe) || usb_pipeint(urb->pipe))
>+		lh = &bh->prio_hi_head;
>+	else
>+		lh = &bh->prio_lo_head;
>+
>	spin_lock(&bh->lock);
>-	list_add_tail(&urb->urb_list, &bh->head);
>-	running = bh->running;
>+	list_add_tail(&urb->urb_list, lh);
>	spin_unlock(&bh->lock);
>-
>-	if (running)
>-		;
>-	else if (high_prio_bh)
>-		tasklet_hi_schedule(&bh->bh);
>-	else
>-		tasklet_schedule(&bh->bh);
>}
>EXPORT_SYMBOL_GPL(usb_hcd_giveback_urb);
>
>@@ -2334,8 +2374,17 @@ irqreturn_t usb_hcd_irq (int irq, void *__hcd)
>		rc = IRQ_NONE;
>	else if (hcd->driver->irq(hcd) == IRQ_NONE)
>		rc = IRQ_NONE;
>-	else
>-		rc = IRQ_HANDLED;
>+	else {
>+		struct giveback_urb	*bh = &hcd->gb_urb;
>+
>+		spin_lock(&bh->lock);
>+		if (!list_empty(&bh->prio_hi_head) ||
>+		    !list_empty(&bh->prio_lo_head))
>+			rc = IRQ_WAKE_THREAD;
>+		else
>+			rc = IRQ_HANDLED;
>+		spin_unlock(&bh->lock);
>+	}
>
>	return rc;
>}
>@@ -2410,12 +2459,12 @@ EXPORT_SYMBOL_GPL (usb_hc_died);
>
>/*-------------------------------------------------------------------------*/
>
>-static void init_giveback_urb_bh(struct giveback_urb_bh *bh)
>+static void init_giveback_urb(struct giveback_urb *bh)
>{
>-
>-	spin_lock_init(&bh->lock);
>-	INIT_LIST_HEAD(&bh->head);
>-	tasklet_setup(&bh->bh, usb_giveback_urb_bh);
>+	INIT_LIST_HEAD(&bh->prio_lo_head);
>+	INIT_LIST_HEAD(&bh->prio_hi_head);
>+	INIT_LIST_HEAD(&bh->rh_head);
>+	INIT_WORK(&bh->rh_compl, usb_hcd_rh_gb_urb);
>}
>
>struct usb_hcd *__usb_create_hcd(const struct hc_driver *driver,
>@@ -2593,8 +2642,9 @@ static int usb_hcd_request_irqs(struct usb_hcd *hcd,
>
>		snprintf(hcd->irq_descr, sizeof(hcd->irq_descr), "%s:usb%d",
>				hcd->driver->description, hcd->self.busnum);
>-		retval = request_irq(irqnum, &usb_hcd_irq, irqflags,
>-				hcd->irq_descr, hcd);
>+		retval = request_threaded_irq(irqnum, &usb_hcd_irq,
>+					      usb_hcd_gb_urb, irqflags,
>+					      hcd->irq_descr, hcd);
>		if (retval != 0) {
>			dev_err(hcd->self.controller,
>					"request interrupt %d failed\n",
>@@ -2783,9 +2833,7 @@ int usb_add_hcd(struct usb_hcd *hcd,
>			&& device_can_wakeup(&hcd->self.root_hub->dev))
>		dev_dbg(hcd->self.controller, "supports USB remote wakeup\n");
>
>-	/* initialize tasklets */
>-	init_giveback_urb_bh(&hcd->high_prio_bh);
>-	init_giveback_urb_bh(&hcd->low_prio_bh);
>+	init_giveback_urb(&hcd->gb_urb);
>
>	/* enable irqs just before we start the controller,
>	 * if the BIOS provides legacy PCI irqs.
>diff --git a/drivers/usb/dwc2/hcd.c b/drivers/usb/dwc2/hcd.c
>index e9ac215b9663..fa6a0e7eb899 100644
>--- a/drivers/usb/dwc2/hcd.c
>+++ b/drivers/usb/dwc2/hcd.c
>@@ -4162,7 +4162,9 @@ void dwc2_host_complete(struct dwc2_hsotg *hsotg, struct dwc2_qtd *qtd,
>	kfree(qtd->urb);
>	qtd->urb = NULL;
>
>+	spin_unlock(&hsotg->lock);
>	usb_hcd_giveback_urb(dwc2_hsotg_to_hcd(hsotg), urb, status);
>+	spin_lock(&hsotg->lock);
>}
>
>/*
>@@ -4902,7 +4904,7 @@ static struct hc_driver dwc2_hc_driver = {
>	.hcd_priv_size = sizeof(struct wrapper_priv_data),
>
>	.irq = _dwc2_hcd_irq,
>-	.flags = HCD_MEMORY | HCD_USB2 | HCD_BH,
>+	.flags = HCD_MEMORY | HCD_USB2,
>
>	.start = _dwc2_hcd_start,
>	.stop = _dwc2_hcd_stop,
>diff --git a/include/linux/usb/hcd.h b/include/linux/usb/hcd.h
>index 96281cd50ff6..15a55aaa0e9c 100644
>--- a/include/linux/usb/hcd.h
>+++ b/include/linux/usb/hcd.h
>@@ -64,11 +64,12 @@
>
>/*-------------------------------------------------------------------------*/
>
>-struct giveback_urb_bh {
>-	bool running;
>+struct giveback_urb {
>	spinlock_t lock;
>-	struct list_head  head;
>-	struct tasklet_struct bh;
>+	struct list_head	prio_lo_head;
>+	struct list_head	prio_hi_head;
>+	struct list_head	rh_head;
>+	struct work_struct	rh_compl;
>	struct usb_host_endpoint *completing_ep;
>};
>
>@@ -179,8 +180,7 @@ struct usb_hcd {
>	resource_size_t		rsrc_len;	/* memory/io resource length */
>	unsigned		power_budget;	/* in mA, 0 = no limit */
>
>-	struct giveback_urb_bh  high_prio_bh;
>-	struct giveback_urb_bh  low_prio_bh;
>+	struct giveback_urb     gb_urb;
>
>	/* bandwidth_mutex should be taken before adding or removing
>	 * any new bus bandwidth constraints:
>@@ -420,7 +420,7 @@ static inline int hcd_giveback_urb_in_bh(struct usb_hcd *hcd)
>static inline bool hcd_periodic_completion_in_progress(struct usb_hcd *hcd,
>		struct usb_host_endpoint *ep)
>{
>-	return hcd->high_prio_bh.completing_ep == ep;
>+	return hcd->gb_urb.completing_ep == ep;
>}
>
>static inline bool hcd_uses_dma(struct usb_hcd *hcd)