Re: [PATCH v4 1/2] usb: gadget: udc: core: Invoke usb_gadget_connect only when started

[Badhri Jagan Sridharan]

Hi Thorsten,

Francesso  had shared the stack dump as well at
https://lore.kernel.org/all/ZGMm2sxN6wW%2FEWrR@xxxxxxxxxxxxxxxxxxxxxxxxxxxx/.
I am working on a fix based on that. Going to share it in the next
hour and would be requesting Franceso and others help to see if the
regression goes away.

Thanks,
Badhri


On Wed, May 17, 2023 at 3:23 AM Linux regression tracking (Thorsten
Leemhuis) <regressions@xxxxxxxxxxxxx> wrote:
>
> [CCing Francesco Dolcini; and the regression list too, as it should be
> in the loop for regressions:
> https://docs.kernel.org/admin-guide/reporting-regressions.html]
>
> On 16.05.23 14:53, Alistair wrote:
> > On Fri, 2023-04-07 at 03:07 +0000, Badhri Jagan Sridharan wrote:
> >> usb_udc_connect_control does not check to see if the udc has already
> >> been started. This causes gadget->ops->pullup to be called through
> >> usb_gadget_connect when invoked from usb_udc_vbus_handler even before
> >> usb_gadget_udc_start is called. Guard this by checking for udc-
> >>> started
> >> in usb_udc_connect_control before invoking usb_gadget_connect.
> > [...]
> >> Cc: stable@xxxxxxxxxxxxxxx
> >> Fixes: 628ef0d273a6 ("usb: udc: add usb_udc_vbus_handler")
> >> Signed-off-by: Badhri Jagan Sridharan <badhri@xxxxxxxxxx>
> >
> > This patch causes a kernel hang when trying to boot with the
> > usb/chipidea/udc.c driver.
> >
> > The call stack below causes the hang:
> >
> >  - gadget_bind_driver(struct device *dev)
> >     - mutex_lock(&udc->connect_lock);
> >     - usb_gadget_udc_start_locked(struct usb_udc *udc)
> >         - udc->gadget->ops->udc_start(udc->gadget, udc->driver)
> >
> > At which point we are calling ci_udc_start(..), but with the
> > connect_lock mutex locked.
> >
> > ci_udc_start() then calls usb_udc_vbus_handler() which tries to lock
> > the connect_lock while it's already locked. Resulting in a kernel hang.
> >
> > Reverting this patch fixes the hang.
>
> Not my area of expertise, but I guess it might be the same error as this
> one:
>
> https://lore.kernel.org/all/ZF4BvgsOyoKxdPFF@xxxxxxxxxxxxxxxxxxxxxxxxxxxx/
>
> Francesco sent a revert on Friday, but no reaction from Badhri Jagan
> Sridharan or Greg yet afaics.
>
> https://lore.kernel.org/all/20230512131435.205464-1-francesco@xxxxxxxxxx/
>
> Ciao, Thorsten