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Message-ID: <20210625163707.GC574023@rowland.harvard.edu>
Date: Fri, 25 Jun 2021 12:37:07 -0400
From: Alan Stern <stern@...land.harvard.edu>
To: Linyu Yuan <linyyuan@...eaurora.org>
Cc: Felipe Balbi <balbi@...nel.org>,
Thinh Nguyen <Thinh.Nguyen@...opsys.com>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
Jack Pham <jackp@...eaurora.org>
Subject: Re: [PATCH] usb: dwc3: fix race of usb_gadget_driver operation
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 <linyyuan@...eaurora.org>
> ---
> 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).
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
>
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