On 2018-06-14 10:44:20 [+0200], Oliver Neukum wrote:
> On Mi, 2018-06-13 at 22:28 +0200, Sebastian Andrzej Siewior wrote:
> > On 2018-06-13 19:43:55 [+0200], Oliver Neukum wrote:
> Hi Sebastian,
Hi Oliver,
> > > I am just looking at your patch and I am wondering why
> > > wdm_in_callback() won't just call service_outstanding_interrupt()
> > > again and again? OK, maybe I am dense and it may well be present now,
> > > but it just looks to me that way.
> >
> > But this part didn't change, did it?
>
> Right, it didn't change, but that does not make it correct.
Yes, I just wanted make sure that the breakage is not part of the patch.
> > The user blocks in wdmw_read()
>
> We can only hope that he does. The wait is interruptible.
> If a signal comes at the wrong time, nobody will be waiting.
>
> > Maybe we should delay the WDM_READ flag in the error case until the
> > worker is done (before the wakeup).
>
> I don't think that will help.
Why not? If it won't see WDM_READ flag set then it will return with
-EBUSY.
> It seems like we need to make sure
> that error recovery is a one shot activity.
I think it will be if we delay the WDM_READ because the user will not be
aware of the situation until the error recovery is done and not after
the URB has been submitted:
--->8
Subject: [PATCH v3] USB: cdc-wdm: don't enable interrupts in USB-giveback
In the code path
__usb_hcd_giveback_urb()
-> wdm_in_callback()
-> service_outstanding_interrupt()
The function service_outstanding_interrupt() will unconditionally enable
interrupts during unlock and invoke usb_submit_urb() with GFP_KERNEL.
If the HCD completes in BH (like ehci does) then the context remains
atomic due local_bh_disable() and enabling interrupts does not change
this.
Defer the error case handling to a workqueue as suggested by Oliver
Neukum. In case of an error the worker performs the read out and wakes
the user.
Fixes: c1da59dad0eb ("cdc-wdm: Clear read pipeline in case of error")
Cc: Robert Foss <robert.foss@xxxxxxxxxxxxx>
Cc: Oliver Neukum <oneukum@xxxxxxxx>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
---
v2…v3: set WDM_READ once error recovery is done so the user does not see
WDM_READ before the _last_ submitted.
v1…v2: invoke service_outstanding_interrupt() from a worker
drivers/usb/class/cdc-wdm.c | 25 +++++++++++++++++++------
1 file changed, 19 insertions(+), 6 deletions(-)
diff --git a/drivers/usb/class/cdc-wdm.c b/drivers/usb/class/cdc-wdm.c
index a0d284ef3f40..ddf55f93d4ca 100644
--- a/drivers/usb/class/cdc-wdm.c
+++ b/drivers/usb/class/cdc-wdm.c
@@ -96,6 +96,7 @@ struct wdm_device {
struct mutex rlock;
wait_queue_head_t wait;
struct work_struct rxwork;
+ struct work_struct service_outs_intr;
int werr;
int rerr;
int resp_count;
@@ -151,9 +152,6 @@ static void wdm_out_callback(struct urb *urb)
wake_up(&desc->wait);
}
-/* forward declaration */
-static int service_outstanding_interrupt(struct wdm_device *desc);
-
static void wdm_in_callback(struct urb *urb)
{
struct wdm_device *desc = urb->context;
@@ -210,7 +208,6 @@ static void wdm_in_callback(struct urb *urb)
}
skip_error:
set_bit(WDM_READ, &desc->flags);
- wake_up(&desc->wait);
if (desc->rerr) {
/*
@@ -219,9 +216,10 @@ static void wdm_in_callback(struct urb *urb)
* We should respond to further attempts from the device to send
* data, so that we can get unstuck.
*/
- service_outstanding_interrupt(desc);
+ schedule_work(&desc->service_outs_intr);
+ } else {
+ wake_up(&desc->wait);
}
-
spin_unlock(&desc->iuspin);
}
@@ -758,6 +756,18 @@ static void wdm_rxwork(struct work_struct *work)
}
}
+static void service_interrupt_work(struct work_struct *work)
+{
+ struct wdm_device *desc;
+
+ desc = container_of(work, struct wdm_device, service_outs_intr);
+
+ spin_lock_irq(&desc->iuspin);
+ service_outstanding_interrupt(desc);
+ wake_up(&desc->wait);
+ spin_unlock_irq(&desc->iuspin);
+}
+
/* --- hotplug --- */
static int wdm_create(struct usb_interface *intf, struct usb_endpoint_descriptor *ep,
@@ -779,6 +789,7 @@ static int wdm_create(struct usb_interface *intf, struct usb_endpoint_descriptor
desc->inum = cpu_to_le16((u16)intf->cur_altsetting->desc.bInterfaceNumber);
desc->intf = intf;
INIT_WORK(&desc->rxwork, wdm_rxwork);
+ INIT_WORK(&desc->service_outs_intr, service_interrupt_work);
rv = -EINVAL;
if (!usb_endpoint_is_int_in(ep))
@@ -964,6 +975,7 @@ static void wdm_disconnect(struct usb_interface *intf)
mutex_lock(&desc->wlock);
kill_urbs(desc);
cancel_work_sync(&desc->rxwork);
+ cancel_work_sync(&desc->service_outs_intr);
mutex_unlock(&desc->wlock);
mutex_unlock(&desc->rlock);
@@ -1065,6 +1077,7 @@ static int wdm_pre_reset(struct usb_interface *intf)
mutex_lock(&desc->wlock);
kill_urbs(desc);
cancel_work_sync(&desc->rxwork);
+ cancel_work_sync(&desc->service_outs_intr);
return 0;
}
--
2.17.1
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