Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751732Ab2JARsI (ORCPT ); Mon, 1 Oct 2012 13:48:08 -0400 Received: from iolanthe.rowland.org ([192.131.102.54]:36027 "HELO iolanthe.rowland.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1751407Ab2JARsG (ORCPT ); Mon, 1 Oct 2012 13:48:06 -0400 Date: Mon, 1 Oct 2012 13:48:05 -0400 (EDT) From: Alan Stern X-X-Sender: stern@iolanthe.rowland.org To: Octavian Purdila cc: Greg Kroah-Hartman , Sarah Sharp , , Subject: Re: [PATCH] usb hub: send clear_tt_buffer_complete events when canceling TT clear work In-Reply-To: Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1545 Lines: 37 On Mon, 1 Oct 2012, Alan Stern wrote: > On Mon, 1 Oct 2012, Octavian Purdila wrote: > > > There is a race condition in the USB hub code with regard to handling > > TT clear requests that can get the HCD driver in a deadlock. Usually > > when an TT clear request is scheduled it will be executed immediately: > > > However, if a suspend operation is triggered before hub_tt_work is > > scheduled, hub_quiesce will cancel the work without notifying the HCD > > driver: > > Ah, this is a very good point. > > > When the device will resume the EHCI driver will get stuck in > > ehci_endpoint_disable waiting for the tt_clearing flag to reset: > > > This patch notifies the HCD driver via clear_tt_buffer_complete > > when canceling TT clear work so that the EHCI driver has a chance to > > clear its tt_clearing flag. > > But I don't like the proposed fix. What we really need to do is avoid > suspending the device until the clear-tt-buffer operation is complete. > Can you write a patch to do that instead? Actually, it would be sufficient to avoid suspending the _hub_ until the clear-tt-buffer operation is complete. In short, hub_quiesce() should wait until all pending TT operations have finished. The cancel_work_sync() call should be replaced with flush_work_sync(). Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/