Re: [v2 PATCH] usb: dwc3: core: remove lock of otg mode during gadget suspend/resume to avoid deadlock

Michael Nazzareno Trimarchi
2024-06-18T22:55:38Z

Hi

On Wed, Jun 19, 2024 at 12:42 AM Thinh Nguyen <Thinh.Nguyen@synopsys.com> wrote:
>
> Hi,
>
> On Wed, Jun 19, 2024, Michael Nazzareno Trimarchi wrote:
> > Hi
> >
> > On Tue, Jun 18, 2024 at 11:55 PM Thinh Nguyen <Thinh.Nguyen@synopsys.com> wrote:
> > >
> > > On Tue, Jun 18, 2024, Meng Li wrote:
> > > > When config CONFIG_USB_DWC3_DUAL_ROLE is selected, and trigger system
> > > > to enter suspend status with below command:
> > > > echo mem > /sys/power/state
> > > > There will be a deadlock issue occurring. Detailed invoking path as
> > > > below:
> > > > dwc3_suspend_common()
> > > > spin_lock_irqsave(&dwc->lock, flags); <-- 1st
> > > > dwc3_gadget_suspend(dwc);
> > > > dwc3_gadget_soft_disconnect(dwc);
> > > > spin_lock_irqsave(&dwc->lock, flags); <-- 2nd
> >
> >
> > In resume path the spinlock was taken too and I see that there is a call
> > dwc3_gadget_soft_connect that call the dwc3_core_soft_reset that can poll
> > using msleep for time. I don't know if this is a valid fix but seems
> > does not fix
> > only commit c7ebd8149ee5
> >
>
> Meng did take the resume path into account. Can you clarify what you
> meant with "does not fix only commit c7ebd8149ee5"?

I have seen that is suppose to fix something introduced by that commit
but I think
that resume path was already broken before

spinlock_irqsave()
dwc3_gadget_resume -> dwc3_gadget_soft_connect -> dwc3_core_soft_reset
(can sleep)

Michael
>
> Thanks,
> Thinh
>
> >
> > > > This issue is exposed by commit c7ebd8149ee5 ("usb: dwc3: gadget: Fix
> > > > NULL pointer dereference in dwc3_gadget_suspend") that removes the code
> > > > of checking whether dwc->gadget_driver is NULL or not. It causes the
> > > > following code is executed and deadlock occurs when trying to get the
> > > > spinlock. In fact, the root cause is the commit 5265397f9442("usb: dwc3:
> > > > Remove DWC3 locking during gadget suspend/resume") that forgot to remove
> > > > the lock of otg mode. So, remove the redundant lock of otg mode during
> > > > gadget suspend/resume.
> > > >
> > > > Fixes: 5265397f9442 ("usb: dwc3: Remove DWC3 locking during gadget suspend/resume")
> > > > Cc: Xu Yang <xu.yang_2@nxp.com>
> > > > Cc: stable@vger.kernel.org
> > > > Signed-off-by: Meng Li <Meng.Li@windriver.com>
> > > >
> > > > ---
> > > > v1->v2:
> > > > - improve commit log, correct the Fixes commit id.
> > > >
> > > > ---
> > > > drivers/usb/dwc3/core.c | 6 ------
> > > > 1 file changed, 6 deletions(-)
> > > >
> > > > diff --git a/drivers/usb/dwc3/core.c b/drivers/usb/dwc3/core.c
> > > > index 7ee61a89520b..9d47c3aa5777 100644
> > > > --- a/drivers/usb/dwc3/core.c
> > > > +++ b/drivers/usb/dwc3/core.c
> > > > @@ -2250,7 +2250,6 @@ static int dwc3_core_init_for_resume(struct dwc3 *dwc)
> > > >
> > > > static int dwc3_suspend_common(struct dwc3 *dwc, pm_message_t msg)
> > > > {
> > > > - unsigned long flags;
> > > > u32 reg;
> > > > int i;
> > > >
> > > > @@ -2293,9 +2292,7 @@ static int dwc3_suspend_common(struct dwc3 *dwc, pm_message_t msg)
> > > > break;
> > > >
> > > > if (dwc->current_otg_role == DWC3_OTG_ROLE_DEVICE) {
> > > > - spin_lock_irqsave(&dwc->lock, flags);
> > > > dwc3_gadget_suspend(dwc);
> > > > - spin_unlock_irqrestore(&dwc->lock, flags);
> > > > synchronize_irq(dwc->irq_gadget);
> > > > }
> > > >
> > > > @@ -2312,7 +2309,6 @@ static int dwc3_suspend_common(struct dwc3 *dwc, pm_message_t msg)
> > > >
> > > > static int dwc3_resume_common(struct dwc3 *dwc, pm_message_t msg)
> > > > {
> > > > - unsigned long flags;
> > > > int ret;
> > > > u32 reg;
> > > > int i;
> > > > @@ -2366,9 +2362,7 @@ static int dwc3_resume_common(struct dwc3 *dwc, pm_message_t msg)
> > > > if (dwc->current_otg_role == DWC3_OTG_ROLE_HOST) {
> > > > dwc3_otg_host_init(dwc);
> > > > } else if (dwc->current_otg_role == DWC3_OTG_ROLE_DEVICE) {
> > > > - spin_lock_irqsave(&dwc->lock, flags);
> > > > dwc3_gadget_resume(dwc);
> > > > - spin_unlock_irqrestore(&dwc->lock, flags);
> > > > }
> > > >
> > > > break;
> > > > --
> > > > 2.34.1
> > > >
> > >
> > > Did you use "git format-patch -v"? The $subject version prefix order is
> > > different. In any case,
> > >
> > > Acked-by: Thinh Nguyen <Thinh.Nguyen@synopsys.com>
> > >
> > > Thanks,
> > > Thinh

--
Michael Nazzareno Trimarchi
Co-Founder & Chief Executive Officer
M. +39 347 913 2170
michael@amarulasolutions.com
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