On Mon, 26 Mar 2018, Felipe Balbi wrote: > Mention that ->complete() should never be called from within > usb_ep_queue(). > > Signed-off-by: Felipe Balbi <felipe.balbi@xxxxxxxxxxxxxxx> > --- > drivers/usb/gadget/udc/core.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/drivers/usb/gadget/udc/core.c b/drivers/usb/gadget/udc/core.c > index 50988b21a21b..842814bc0e4f 100644 > --- a/drivers/usb/gadget/udc/core.c > +++ b/drivers/usb/gadget/udc/core.c > @@ -238,6 +238,9 @@ EXPORT_SYMBOL_GPL(usb_ep_free_request); > * arranges to poll once per interval, and the gadget driver usually will > * have queued some data to transfer at that time. > * > + * Note that @req's ->complete() callback must never be called from > + * within usb_ep_queue() as that can create deadlock situations. > + * I think this is highly questionable. Certainly it was not David Brownell's original intention; his dummy-hcd driver will sometimes give back a request from within usb_ep_queue() -- and I believe he wrote it that way in order to emulate a feature of his net2280 driver. In this particular case, the problem is that a driver acquires a spinlock in its complete() routine, but then it holds that same spinlock while submitting a request. This is a bug; it should be fixed in the driver. The spinlock should be dropped while the request is submitted. I'm sure there are examples whether other drivers do this. Alan Stern -- 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
