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Sat, 26 Jun 2021 01:16:26 +0000 (UTC) Received: from mail.codeaurora.org (localhost.localdomain [127.0.0.1]) (using TLSv1 with cipher ECDHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) (Authenticated sender: linyyuan) by smtp.codeaurora.org (Postfix) with ESMTPSA id C8D96C433D3; Sat, 26 Jun 2021 01:16:25 +0000 (UTC) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII; format=flowed Content-Transfer-Encoding: 7bit Date: Sat, 26 Jun 2021 09:16:25 +0800 From: linyyuan@codeaurora.org To: Alan Stern Cc: Felipe Balbi , Thinh Nguyen , Greg Kroah-Hartman , linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org, Jack Pham Subject: Re: [PATCH] usb: dwc3: fix race of usb_gadget_driver operation In-Reply-To: <20210625163707.GC574023@rowland.harvard.edu> References: <20210625104415.8072-1-linyyuan@codeaurora.org> <20210625163707.GC574023@rowland.harvard.edu> Message-ID: X-Sender: linyyuan@codeaurora.org User-Agent: Roundcube Webmail/1.3.9 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2021-06-26 00:37, Alan Stern wrote: > On Fri, Jun 25, 2021 at 06:44:15PM +0800, Linyu Yuan wrote: >> there is following race condition, >> >> CPU1 CPU2 >> dwc3_runtime_suspend() dwc3_gadget_stop() >> spin_lock(&dwc->lock) >> dwc3_gadget_suspend() >> dwc3_disconnect_gadget() >> dwc->gadget_driver != NULL >> spin_unlock(&dwc->lock) >> spin_lock(&dwc->lock) >> dwc->gadget_driver = NULL >> spin_unlock(&dwc->lock) >> dwc->gadget_driver->disconnect(dwc->gadget); >> >> system will crash when access NULL gadget_driver. >> >> 7dc0c55e9f30 ('USB: UDC core: Add udc_async_callbacks gadget op') >> suggest a common way to avoid such kind of race. >> >> this change implment the callback in dwc3 and >> change related functions which have callback to UDC core. >> >> Signed-off-by: Linyu Yuan >> --- >> drivers/usb/dwc3/core.h | 1 + >> drivers/usb/dwc3/ep0.c | 5 +++-- >> drivers/usb/dwc3/gadget.c | 39 >> +++++++++++++++++++++++---------------- >> 3 files changed, 27 insertions(+), 18 deletions(-) >> >> diff --git a/drivers/usb/dwc3/core.h b/drivers/usb/dwc3/core.h >> index dccdf13b5f9e..5991766239ba 100644 >> --- a/drivers/usb/dwc3/core.h >> +++ b/drivers/usb/dwc3/core.h >> @@ -1279,6 +1279,7 @@ struct dwc3 { >> unsigned dis_metastability_quirk:1; >> >> unsigned dis_split_quirk:1; >> + unsigned async_callbacks:1; >> >> u16 imod_interval; >> }; >> diff --git a/drivers/usb/dwc3/ep0.c b/drivers/usb/dwc3/ep0.c >> index 3cd294264372..26419077c7c9 100644 >> --- a/drivers/usb/dwc3/ep0.c >> +++ b/drivers/usb/dwc3/ep0.c >> @@ -597,10 +597,11 @@ static int dwc3_ep0_set_address(struct dwc3 >> *dwc, struct usb_ctrlrequest *ctrl) >> >> static int dwc3_ep0_delegate_req(struct dwc3 *dwc, struct >> usb_ctrlrequest *ctrl) >> { >> - int ret; >> + int ret = 0; >> >> spin_unlock(&dwc->lock); >> - ret = dwc->gadget_driver->setup(dwc->gadget, ctrl); >> + if (dwc->async_callbacks) >> + ret = dwc->gadget_driver->setup(dwc->gadget, ctrl); >> spin_lock(&dwc->lock); > > Here and in the other places, you should test dwc->async_callbacks > _before_ dropping the spinlock. Otherwise there is a race (the flag > could be written at about the same time it is checked). thanks for your comments, if you think there is race here, how to make sure gadget_driver pointer is safe, this is closest place where we can confirm it is non-NULL by checking async_callbacks ? > > Alan Stern > >> return ret; >> } >> diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c >> index af6d7f157989..d868f30007cc 100644 >> --- a/drivers/usb/dwc3/gadget.c >> +++ b/drivers/usb/dwc3/gadget.c >> @@ -2585,6 +2585,16 @@ static int dwc3_gadget_vbus_draw(struct >> usb_gadget *g, unsigned int mA) >> return ret; >> } >> >> +static void dwc3_gadget_async_callbacks(struct usb_gadget *g, bool >> enable) >> +{ >> + struct dwc3 *dwc = gadget_to_dwc(g); >> + unsigned long flags; >> + >> + spin_lock_irqsave(&dwc->lock, flags); >> + dwc->async_callbacks = enable; >> + spin_unlock_irqrestore(&dwc->lock, flags); >> +} >> + >> static const struct usb_gadget_ops dwc3_gadget_ops = { >> .get_frame = dwc3_gadget_get_frame, >> .wakeup = dwc3_gadget_wakeup, >> @@ -2596,6 +2606,7 @@ static const struct usb_gadget_ops >> dwc3_gadget_ops = { >> .udc_set_ssp_rate = dwc3_gadget_set_ssp_rate, >> .get_config_params = dwc3_gadget_config_params, >> .vbus_draw = dwc3_gadget_vbus_draw, >> + .udc_async_callbacks = dwc3_gadget_async_callbacks, >> }; >> >> /* >> -------------------------------------------------------------------------- >> */ >> @@ -3231,29 +3242,26 @@ static void dwc3_endpoint_interrupt(struct >> dwc3 *dwc, >> >> static void dwc3_disconnect_gadget(struct dwc3 *dwc) >> { >> - if (dwc->gadget_driver && dwc->gadget_driver->disconnect) { >> - spin_unlock(&dwc->lock); >> + spin_unlock(&dwc->lock); >> + if (dwc->async_callbacks && dwc->gadget_driver->disconnect) >> dwc->gadget_driver->disconnect(dwc->gadget); >> - spin_lock(&dwc->lock); >> - } >> + spin_lock(&dwc->lock); >> } >> >> static void dwc3_suspend_gadget(struct dwc3 *dwc) >> { >> - if (dwc->gadget_driver && dwc->gadget_driver->suspend) { >> - spin_unlock(&dwc->lock); >> + spin_unlock(&dwc->lock); >> + if (dwc->async_callbacks && dwc->gadget_driver->suspend) >> dwc->gadget_driver->suspend(dwc->gadget); >> - spin_lock(&dwc->lock); >> - } >> + spin_lock(&dwc->lock); >> } >> >> static void dwc3_resume_gadget(struct dwc3 *dwc) >> { >> - if (dwc->gadget_driver && dwc->gadget_driver->resume) { >> - spin_unlock(&dwc->lock); >> + spin_unlock(&dwc->lock); >> + if (dwc->async_callbacks && dwc->gadget_driver->resume) >> dwc->gadget_driver->resume(dwc->gadget); >> - spin_lock(&dwc->lock); >> - } >> + spin_lock(&dwc->lock); >> } >> >> static void dwc3_reset_gadget(struct dwc3 *dwc) >> @@ -3585,11 +3593,10 @@ static void >> dwc3_gadget_wakeup_interrupt(struct dwc3 *dwc) >> * implemented. >> */ >> >> - if (dwc->gadget_driver && dwc->gadget_driver->resume) { >> - spin_unlock(&dwc->lock); >> + spin_unlock(&dwc->lock); >> + if (dwc->async_callbacks && dwc->gadget_driver->resume) >> dwc->gadget_driver->resume(dwc->gadget); >> - spin_lock(&dwc->lock); >> - } >> + spin_lock(&dwc->lock); >> } >> >> static void dwc3_gadget_linksts_change_interrupt(struct dwc3 *dwc, >> -- >> 2.25.1 >>