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=-11.5 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=unavailable 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 AD366C433E0 for ; Fri, 31 Jul 2020 14:22:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 94ECC21744 for ; Fri, 31 Jul 2020 14:22:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729184AbgGaOWN (ORCPT ); Fri, 31 Jul 2020 10:22:13 -0400 Received: from netrider.rowland.org ([192.131.102.5]:56885 "HELO netrider.rowland.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1729172AbgGaOWN (ORCPT ); Fri, 31 Jul 2020 10:22:13 -0400 Received: (qmail 37750 invoked by uid 1000); 31 Jul 2020 10:22:12 -0400 Date: Fri, 31 Jul 2020 10:22:12 -0400 From: Alan Stern To: Macpaul Lin Cc: Chunfeng Yun , Eddie Hung , Greg Kroah-Hartman , Matthias Brugger , linux-usb@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-mediatek@lists.infradead.org, linux-kernel@vger.kernel.org, Mediatek WSD Upstream , Macpaul Lin , stable@vger.kernel.org Subject: Re: [PATCH v2] usb: mtu3: fix panic in mtu3_gadget_disconnect() Message-ID: <20200731142212.GE36650@rowland.harvard.edu> References: <1596177366-12029-1-git-send-email-macpaul.lin@mediatek.com> <1596185878-24360-1-git-send-email-macpaul.lin@mediatek.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1596185878-24360-1-git-send-email-macpaul.lin@mediatek.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-usb-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-usb@vger.kernel.org On Fri, Jul 31, 2020 at 04:57:58PM +0800, Macpaul Lin wrote: > This patch fixes a possible issue when mtu3_gadget_stop() > already assigned NULL to mtu->gadget_driver during mtu_gadget_disconnect(). > > Signed-off-by: Macpaul Lin > Cc: stable@vger.kernel.org > --- > Changes for v2: > - Check mtu_gadget_driver out of spin_lock might still not work. > We use a temporary pointer to keep the callback function. > > drivers/usb/mtu3/mtu3_gadget.c | 9 ++++++++- > 1 file changed, 8 insertions(+), 1 deletion(-) > > diff --git a/drivers/usb/mtu3/mtu3_gadget.c b/drivers/usb/mtu3/mtu3_gadget.c > index 68ea4395f871..40cb6626f496 100644 > --- a/drivers/usb/mtu3/mtu3_gadget.c > +++ b/drivers/usb/mtu3/mtu3_gadget.c > @@ -840,10 +840,17 @@ void mtu3_gadget_suspend(struct mtu3 *mtu) > /* called when VBUS drops below session threshold, and in other cases */ > void mtu3_gadget_disconnect(struct mtu3 *mtu) > { > + struct usb_gadget_driver *driver; > + > dev_dbg(mtu->dev, "gadget DISCONNECT\n"); > if (mtu->gadget_driver && mtu->gadget_driver->disconnect) { > + driver = mtu->gadget_driver; > spin_unlock(&mtu->lock); > - mtu->gadget_driver->disconnect(&mtu->g); > + /* > + * avoid kernel panic because mtu3_gadget_stop() assigned NULL > + * to mtu->gadget_driver. > + */ > + driver->disconnect(&mtu->g); > spin_lock(&mtu->lock); > } This is not the right approach; it might race with the gadget driver unregistering itself. Instead, mtu3_gadget_stop() should call synchronize_irq() after releasing the IRQ line. When synchronize_irq() returns, you'll know any IRQ handlers have finished running, so you won't receive any more disconnect notifications. Then it will be safe to acquire the spinlock and set mtu->gadget_driver to NULL. Alan Stern