From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_2 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 48C98C0650E for ; Thu, 4 Jul 2019 21:44:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 193952184B for ; Thu, 4 Jul 2019 21:44:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726273AbfGDVox (ORCPT ); Thu, 4 Jul 2019 17:44:53 -0400 Received: from gate.crashing.org ([63.228.1.57]:47761 "EHLO gate.crashing.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725917AbfGDVox (ORCPT ); Thu, 4 Jul 2019 17:44:53 -0400 Received: from localhost (localhost.localdomain [127.0.0.1]) by gate.crashing.org (8.14.1/8.14.1) with ESMTP id x64LifPd031202; Thu, 4 Jul 2019 16:44:42 -0500 Message-ID: <776c8b72bff0d7dc80d56e58a0c8c1f46b882eb5.camel@kernel.crashing.org> Subject: Re: Virtual hub, resets etc... From: Benjamin Herrenschmidt To: Alan Stern Cc: Felipe Balbi , "linux-usb@vger.kernel.org" , Michal Nazarewicz Date: Fri, 05 Jul 2019 07:44:39 +1000 In-Reply-To: References: Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.28.5-0ubuntu0.18.04.1 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-usb-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-usb@vger.kernel.org On Thu, 2019-07-04 at 12:13 -0400, Alan Stern wrote: > > - bus reset: When I sense a bus reset, that's where I'm not too sure > > what to do. Currently I clear all the status bits of the ports > > except USB_PORT_STAT_SUSPEND. Thus I clear USB_PORT_STAT_ENABLE. > > But I'm not sure what to do with the gadget. I currently call > > the gadget suspend as "hinted" by the spec calling for S0 state iirc, > > but I don't think it's the best thing to do, it doesn't make that much > > sense... Should I do a gadget reset instead ? > > You should also clear USB_PORT_STAT_SUSPEND. Calling the gadget's > suspend routine (if the gadget isn't already suspended) is the right > thing to do; the spec says a USB device goes into suspend if it doesn't > receive any packets for a period of 3 (or 5? -- something like that) > ms, and that certainly would be the case here. > > > - If the host clears USB_PORT_STAT_ENABLE, what should I do ? I > > currently do a suspend as well, which isn't great... mostly it does > > nothing and keep potentially the gadget trying to do stuff. I could > > do a reset. I don't want to do a disconnect because we are still > > connected to the hub so that's not really the right call, but at least > > for composite it's the same thing... > > As above, doing a suspend is the right thing. It is the right HW behaviour. But with our gadget stack, it doesn't reset or cleanup anything. Though since the port gets disabled, I suppose re-enabling it will cause a reset and will sort that out. > > Now, a few things i noticed while at it: > > > > - At some point I had code to reject EP queue() if the device is > > suspended with -ESHUTDOWN. The end result was bad ... f_mass_storage > > goes into an infinite loop of trying to queue the same stuff in > > start_out_transfer() when that happens. It looks like it's not really > > handling errors from queue() in a particularily useful way. > > Don't reject EP queue requests. Accept them as you would at any time; > they will complete after the port is resumed. Except the suspend on a bus reset clears the port enable. You can't resume from that, only reset the port no ? Or am I missing something ? > As for f_mass_storage, repeatedly attempting to queue an OUT transfer > is normal behavior. The fact that one attempt gets an error doesn't > stop the driver from making more attempts; the only thing that would > stop it is being disabled by a config change, a suspend, a disconnect, > or an unbind. Except it does that in a tight loop and locks up the machine... > > - With my current code doing suspend/resume on bus resets, when I > > reboot some hosts, and they re-enumerate, I tend to hit the WARN_ON > > drivers/usb/gadget/function/f_mass_storage.c:341 > > > > static inline int __fsg_is_set(struct fsg_common *common, > > const char *func, unsigned line) > > { > > if (common->fsg) > > return 1; > > ERROR(common, "common->fsg is NULL in %s at %u\n", func, line); > > WARN_ON(1); > > return 0; > > } > > > > This happens a little while after a successul set_configuration. Here's > > a trace: > > ... > > > I have to get my head around that code, but if one of you have a clue, I > > would welcome it :-) > > > > Interestingly it recovers. The host seems to then reset the prot, then reconfigure and > > the second time around it all works fine. > > I suspect this is related to the race you found. EJ Hsu has been > working on much the same thing (see the mailing list archive). Right. I debugged the race and produced the fix I posted *after* I had change my code to do a reset rather than a suspend on the hub receiving an upstream bus reset. I will switch back to doing suspend instead and see whether that stays fixed. Cheers, Ben.