The kernel doc entry for usb_unlink_urb() contains the phrase "This request is always asynchronous.". The "always" leads to the assumption that the ->complete() callback is not called from within usb_unlink_urb(). This is not true. The HCD is allowed to call the ->complete() from within ->urb_dequeue() if it is appropriate for the hardware. This patch updates the kernel doc so usb-device driver authors make sure to drop all locks (and make sure it is okay to drop them) which are acquired by the complete callback before calling usb_unlink_urb(). Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> --- v1..v2: - add Alan's suggestion - s/hcd/HCD drivers/usb/core/urb.c | 11 +++++++---- 1 files changed, 7 insertions(+), 4 deletions(-) diff --git a/drivers/usb/core/urb.c b/drivers/usb/core/urb.c index f4f20c7..7239a73 100644 --- a/drivers/usb/core/urb.c +++ b/drivers/usb/core/urb.c @@ -527,10 +527,13 @@ EXPORT_SYMBOL_GPL(usb_submit_urb); * a driver's I/O routines to insure that all URB-related activity has * completed before it returns. * - * This request is always asynchronous. Success is indicated by - * returning -EINPROGRESS, at which time the URB will probably not yet - * have been given back to the device driver. When it is eventually - * called, the completion function will see @urb->status == -ECONNRESET. + * This request is asynchronous, however the HCD might call the ->complete() + * callback during unlink. Therefore when drivers call usb_unlink_urb(), they + * must not hold any locks that may be taken by the completion function. + * Success is indicated by returning -EINPROGRESS, at which time the URB will + * probably not yet have been given back to the device driver. When it is + * eventually called, the completion function will see @urb->status == + * -ECONNRESET. * Failure is indicated by usb_unlink_urb() returning any other value. * Unlinking will fail when @urb is not currently "linked" (i.e., it was * never submitted, or it was unlinked before, or the hardware is already -- 1.7.9 -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
