[PATCH v2] USB: cdc-wdm: don't enable interrupts in USB-giveback

[Sebastian Andrzej Siewior]

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.f...@collabora.com>
Cc: Oliver Neukum <oneu...@suse.com>
Signed-off-by: Sebastian Andrzej Siewior <bige...@linutronix.de>
---
On 2018-06-13 10:30:18 [+0200], Oliver Neukum wrote:
> It seems to me that the core of the problem is handling an error
> in irq context potentially. How about shifting it to a work queue?

Something like this then?

 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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