On Tue, Oct 26, 2021 at 12:40:04PM -0700, Wesley Cheng wrote:
> Hi Alan,
>
> On 10/26/2021 7:41 AM, Alan Stern wrote:
> > On Mon, Oct 25, 2021 at 05:44:56PM -0700, Wesley Cheng wrote:
> >> From: Wesley Cheng <wcheng@xxxxxxxxxxxxxx>
> >>
> >> When receiving a disconnect event from the UDC, the mass storage
> >> function driver currently runs the handle_exception() routine
> >> asynchronously. For UDCs that support runtime PM, there is a
> >> possibility the UDC is already suspended by the time the
> >> do_set_interface() is executed. This can lead to HW register access
> >> while the UDC is already suspended.
> >>
> >> Signed-off-by: Wesley Cheng <wcheng@xxxxxxxxxxxxxx>
> >> ---
> >> drivers/usb/gadget/function/f_mass_storage.c | 10 ++++++++++
> >> 1 file changed, 10 insertions(+)
> >>
> >> diff --git a/drivers/usb/gadget/function/f_mass_storage.c b/drivers/usb/gadget/function/f_mass_storage.c
> >> index 3cabf7692ee1..752439690fda 100644
> >> --- a/drivers/usb/gadget/function/f_mass_storage.c
> >> +++ b/drivers/usb/gadget/function/f_mass_storage.c
> >> @@ -2342,6 +2342,16 @@ static void fsg_disable(struct usb_function *f)
> >> {
> >> struct fsg_dev *fsg = fsg_from_func(f);
> >>
> >> + /* Disable the endpoints */
> >> + if (fsg->bulk_in_enabled) {
> >> + usb_ep_disable(fsg->bulk_in);
> >
> > According to the kerneldoc, this routine must be called in process
> > context.
> >
> >> + fsg->bulk_in_enabled = 0;
> >> + }
> >> + if (fsg->bulk_out_enabled) {
> >> + usb_ep_disable(fsg->bulk_out);
> >> + fsg->bulk_out_enabled = 0;
> >> + }
> >> +
> >> __raise_exception(fsg->common, FSG_STATE_CONFIG_CHANGE, NULL);
> >> }
> >
> > Looks like you'll have to find a different way to avoid the problem.
> > For example, if an exception is pending then you might prevent the
> > gadget from going into runtime suspend until the exception has been
> > handled.
> >
> Thanks for the suggestion. I noticed that a lot of other FDs currently
> call usb_ep_disable() in the disable/disconnect path as well. Actually,
> f_mass_storage seems to be the only one that doesn't do so. Maybe we
> should change the kerneldoc :)
You're right; I don't see any real reason why the usb_ep_{en,dis}able
routines can't run in an atomic context. So if you to make this change
to f_mass_storage, you should first submit a patch changing the
kerneldoc.
Alan Stern
