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Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1k1VvN-00076F-1W; Fri, 31 Jul 2020 14:22:17 +0000 Received: from netrider.rowland.org ([192.131.102.5]) by merlin.infradead.org with smtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1k1VvJ-000756-Fj for linux-arm-kernel@lists.infradead.org; Fri, 31 Jul 2020 14:22:14 +0000 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 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-Disposition: inline In-Reply-To: <1596185878-24360-1-git-send-email-macpaul.lin@mediatek.com> User-Agent: Mutt/1.10.1 (2018-07-13) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200731_102213_599332_5BD141CC X-CRM114-Status: GOOD ( 19.15 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-usb@vger.kernel.org, Mediatek WSD Upstream , Greg Kroah-Hartman , Eddie Hung , linux-kernel@vger.kernel.org, stable@vger.kernel.org, Matthias Brugger , linux-mediatek@lists.infradead.org, Chunfeng Yun , Macpaul Lin , linux-arm-kernel@lists.infradead.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.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 _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel