Am Samstag, den 23.01.2021, 11:57 +0900 schrieb Tetsuo Handa:
> On 2021/01/22 0:30, Oliver Neukum wrote:
Hi,
> Right. Shouldn't remaining
>
> kill_urbs(desc);
> cancel_work_sync(&desc->rxwork);
> cancel_work_sync(&desc->service_outs_intr);
>
> sequence in wdm_suspend() and wdm_pre_reset() be updated as well?
Yes, they should.
> > Unfortunately we have in wdm_in_callback() the following code path
> >
> > if (desc->rerr) {
> > /*
> > * Since there was an error, userspace may decide to not read
> > * any data after poll'ing.
> > * We should respond to further attempts from the device to send
> > * data, so that we can get unstuck.
> > */
> > schedule_work(&desc->service_outs_intr);
> >
> > It looks to me like we have a circular dependency here and this needs some
> > change to break. What do you think about the attached patch?
>
> I don't know how poisoning works. But why can't we simply use test_bit() on
It makes subsequent usb_submit_urb() fail.
> WDM_SUSPENDING/WDM_RESETTING/WDM_DISCONNECTING flags, for schedule_work() in
> wdm_in_callback() is called with desc->iuspin (which serializes setting of
> these flags) held.
In theory this could be done, yet that would take three additional
tests as opposed to the test for poisoning that usbcore does anyway.
> By the way, since someone might interpret "broken" as "out of order / not working",
> I expect not using "This needs to be broken." in the commit message. There would be
> some better idiom.
Right. I changed the message.
Could you test whether the attached patch fixes your issue?
Regards
Oliver
From 307097e80657ca44ac99da8efc8397070b1aff3f Mon Sep 17 00:00:00 2001
From: Oliver Neukum <oneukum@xxxxxxxx>
Date: Thu, 18 Feb 2021 13:42:40 +0100
Subject: [PATCH 1/2] cdc-wdm: untangle a circular dependency between callback
and softint
We have a cycle of callbacks scheduling works which submit
URBs with thos callbacks. This needs to be blocked, stopped
and unblocked to untangle the circle..
Signed-off-by: Oliver Neukum <oneukum@xxxxxxxx>
---
drivers/usb/class/cdc-wdm.c | 30 ++++++++++++++++++++++--------
1 file changed, 22 insertions(+), 8 deletions(-)
diff --git a/drivers/usb/class/cdc-wdm.c b/drivers/usb/class/cdc-wdm.c
index 508b1c3f8b73..d1e4a7379beb 100644
--- a/drivers/usb/class/cdc-wdm.c
+++ b/drivers/usb/class/cdc-wdm.c
@@ -321,12 +321,23 @@ static void wdm_int_callback(struct urb *urb)
}
-static void kill_urbs(struct wdm_device *desc)
+static void poison_urbs(struct wdm_device *desc)
{
/* the order here is essential */
- usb_kill_urb(desc->command);
- usb_kill_urb(desc->validity);
- usb_kill_urb(desc->response);
+ usb_poison_urb(desc->command);
+ usb_poison_urb(desc->validity);
+ usb_poison_urb(desc->response);
+}
+
+static void unpoison_urbs(struct wdm_device *desc)
+{
+ /*
+ * the order here is not essential
+ * it is symmetrical just to be nice
+ */
+ usb_unpoison_urb(desc->response);
+ usb_unpoison_urb(desc->validity);
+ usb_unpoison_urb(desc->command);
}
static void free_urbs(struct wdm_device *desc)
@@ -741,11 +752,12 @@ static int wdm_release(struct inode *inode, struct file *file)
if (!desc->count) {
if (!test_bit(WDM_DISCONNECTING, &desc->flags)) {
dev_dbg(&desc->intf->dev, "wdm_release: cleanup\n");
- kill_urbs(desc);
+ poison_urbs(desc);
spin_lock_irq(&desc->iuspin);
desc->resp_count = 0;
spin_unlock_irq(&desc->iuspin);
desc->manage_power(desc->intf, 0);
+ unpoison_urbs(desc);
} else {
/* must avoid dev_printk here as desc->intf is invalid */
pr_debug(KBUILD_MODNAME " %s: device gone - cleaning up\n", __func__);
@@ -1037,9 +1049,9 @@ static void wdm_disconnect(struct usb_interface *intf)
wake_up_all(&desc->wait);
mutex_lock(&desc->rlock);
mutex_lock(&desc->wlock);
+ poison_urbs(desc);
cancel_work_sync(&desc->rxwork);
cancel_work_sync(&desc->service_outs_intr);
- kill_urbs(desc);
mutex_unlock(&desc->wlock);
mutex_unlock(&desc->rlock);
@@ -1080,9 +1092,10 @@ static int wdm_suspend(struct usb_interface *intf, pm_message_t message)
set_bit(WDM_SUSPENDING, &desc->flags);
spin_unlock_irq(&desc->iuspin);
/* callback submits work - order is essential */
- kill_urbs(desc);
+ poison_urbs(desc);
cancel_work_sync(&desc->rxwork);
cancel_work_sync(&desc->service_outs_intr);
+ unpoison_urbs(desc);
}
if (!PMSG_IS_AUTO(message)) {
mutex_unlock(&desc->wlock);
@@ -1140,7 +1153,7 @@ static int wdm_pre_reset(struct usb_interface *intf)
wake_up_all(&desc->wait);
mutex_lock(&desc->rlock);
mutex_lock(&desc->wlock);
- kill_urbs(desc);
+ poison_urbs(desc);
cancel_work_sync(&desc->rxwork);
cancel_work_sync(&desc->service_outs_intr);
return 0;
@@ -1151,6 +1164,7 @@ static int wdm_post_reset(struct usb_interface *intf)
struct wdm_device *desc = wdm_find_device(intf);
int rv;
+ unpoison_urbs(desc);
clear_bit(WDM_OVERFLOW, &desc->flags);
clear_bit(WDM_RESETTING, &desc->flags);
rv = recover_from_urb_loss(desc);
--
2.26.2
