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usb: cdc-wdm: avoid hanging on zero length reads 

commit 73e06865ea ("USB: cdc-wdm: support back-to-back
USB_CDC_NOTIFY_RESPONSE_AVAILABLE notifications") implemented
queued response handling. This added a new requirement: The read
urb must be resubmitted every time we clear the WDM_READ flag if
the response counter indicates that the device is waiting for a
read.

Fix by factoring out the code handling the WMD_READ clearing and
possible urb submission, calling it everywhere we clear the flag.

Without this fix, the driver ends up in a state where the read urb
is inactive, but the response counter is positive after a zero
length read.  This prevents the read urb from ever being submitted
again and the driver appears to be hanging.

Fixes: 73e06865ea ("USB: cdc-wdm: support back-to-back USB_CDC_NOTIFY_RESPONSE_AVAILABLE notifications")
Cc: Greg Suarez <gsuarez@smithmicro.com>
Signed-off-by: Bjørn Mork <bjorn@mork.no>
Cc: stable <stable@vger.kernel.org> # 3.13
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Bjørn Mork 2013-12-20 14:07:24 +01:00 committed by Greg Kroah-Hartman
parent bee53637e5
commit 8dd5cd5395
1 changed files with 38 additions and 32 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

70
drivers/usb/class/cdc-wdm.c
View File

@ -432,6 +432,38 @@ outnl:
return rv < 0 ? rv : count;
}
/*
* clear WDM_READ flag and possibly submit the read urb if resp_count
* is non-zero.
*
* Called with desc->iuspin locked
*/
static int clear_wdm_read_flag(struct wdm_device *desc)
{
int rv = 0;
clear_bit(WDM_READ, &desc->flags);
/* submit read urb only if the device is waiting for it */
if (!--desc->resp_count)
goto out;
set_bit(WDM_RESPONDING, &desc->flags);
spin_unlock_irq(&desc->iuspin);
rv = usb_submit_urb(desc->response, GFP_KERNEL);
spin_lock_irq(&desc->iuspin);
if (rv) {
dev_err(&desc->intf->dev,
"usb_submit_urb failed with result %d\n", rv);
/* make sure the next notification trigger a submit */
clear_bit(WDM_RESPONDING, &desc->flags);
desc->resp_count = 0;
}
out:
return rv;
}
static ssize_t wdm_read
(struct file *file, char __user *buffer, size_t count, loff_t *ppos)
{
@ -503,8 +535,10 @@ retry:
if (!desc->reslength) { /* zero length read */
dev_dbg(&desc->intf->dev, "%s: zero length - clearing WDM_READ\n", __func__);
clear_bit(WDM_READ, &desc->flags);
rv = clear_wdm_read_flag(desc);
spin_unlock_irq(&desc->iuspin);
if (rv < 0)
goto err;
goto retry;
}
cntr = desc->length;
@ -526,37 +560,9 @@ retry:
desc->length -= cntr;
/* in case we had outstanding data */
if (!desc->length) {
clear_bit(WDM_READ, &desc->flags);
if (--desc->resp_count) {
set_bit(WDM_RESPONDING, &desc->flags);
spin_unlock_irq(&desc->iuspin);
rv = usb_submit_urb(desc->response, GFP_KERNEL);
if (rv) {
dev_err(&desc->intf->dev,
"%s: usb_submit_urb failed with result %d\n",
__func__, rv);
spin_lock_irq(&desc->iuspin);
clear_bit(WDM_RESPONDING, &desc->flags);
spin_unlock_irq(&desc->iuspin);
if (rv == -ENOMEM) {
rv = schedule_work(&desc->rxwork);
if (rv)
dev_err(&desc->intf->dev, "Cannot schedule work\n");
} else {
spin_lock_irq(&desc->iuspin);
desc->resp_count = 0;
spin_unlock_irq(&desc->iuspin);
}
}
} else
spin_unlock_irq(&desc->iuspin);
} else
spin_unlock_irq(&desc->iuspin);
if (!desc->length)
clear_wdm_read_flag(desc);
spin_unlock_irq(&desc->iuspin);
rv = cntr;
err: