Re: lockdep warning in urb.c:363 usb_submit_urb

From: "Rafael J. Wysocki" <rafael@kernel.org>
To: Alan Stern <stern@rowland.harvard.edu>
Cc: Qais Yousef <qais.yousef@arm.com>,
	"Rafael J. Wysocki" <rjw@rjwysocki.net>,
	Oliver Neukum <oneukum@suse.de>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	USB list <linux-usb@vger.kernel.org>,
	Linux-pm mailing list <linux-pm@vger.kernel.org>,
	Kernel development list <linux-kernel@vger.kernel.org>
Subject: Re: lockdep warning in urb.c:363 usb_submit_urb
Date: Wed, 25 Mar 2020 22:28:06 +0100	[thread overview]
Message-ID: <CAJZ5v0gqNnoT41=Vm7AtbH8PMW+qPGighK7Up3q2rS+B0jBKFg@mail.gmail.com> (raw)
In-Reply-To: <Pine.LNX.4.44L0.2003251631360.1724-100000@netrider.rowland.org>

On Wed, Mar 25, 2020 at 9:49 PM Alan Stern <stern@rowland.harvard.edu> wrote:
>
> On Wed, 25 Mar 2020, Qais Yousef wrote:
>
> > Thanks for all the hints Alan.
> >
> > I think I figured it out, the below patch seems to fix it for me. Looking
> > at other drivers resume functions it seems we're missing the
> > pm_runtime_disable()->set_active()->enable() dance. Doing that fixes the
> > warning and the dev_err() in driver/base/power.
>
> Ah, yes.  This should have been added years ago; guess I forgot.  :-(
>
> > I don't see xhci-plat.c doing that, I wonder if it needs it too.
> >
> > I'm not well versed about the details and the rules here. So my fix could be
> > a hack, though it does seem the right thing to do.
> >
> > I wonder why the power core doesn't handle this transparently..
>
> Initially, we didn't want the PM core to do this automatically because
> we thought some devices might want to remain runtime-suspended
> following a system resume, and only the device driver would know what
> to do.
>
> Raphael, now that we have the direct_complete mechanism, can we revisit
> this?  Should the PM core automatically call pm_runtime_set_active() if
> dev->power.direct_complete isn't set?  Perhaps in device_resume_early()
> prior to the pm_runtime_enable() call?
>
> It's possible we discussed this and decided against it at the time when
> direct_complete was added, but if so I don't remember what was said.

Me neither. :-)

That said complexity has grown since then and there are the
DPM_FLAG_SMART_SUSPEND and DPM_FLAG_LEAVE_SUSPENDED flags that can be
used to control that behavior to some extent.

Setting DPM_FLAG_SMART_SUSPEND alone, in particular, causes
pm_runtime_set_active() to be called at the noirq stage of device
resume either by the core or by bus types (e.g. PCI) etc.

It looks like ohci-platform might use DPM_FLAG_SMART_SUSPEND, but I
need to take a closer look at that (possibly later this week).

Cheers!

>
> > diff --git a/drivers/usb/host/ohci-platform.c b/drivers/usb/host/ohci-platform.c
> > index 7addfc2cbadc..eb92c8092fae 100644
> > --- a/drivers/usb/host/ohci-platform.c
> > +++ b/drivers/usb/host/ohci-platform.c
> > @@ -299,6 +299,10 @@ static int ohci_platform_resume(struct device *dev)
> >         }
> >
> >         ohci_resume(hcd, false);
> > +
> > +       pm_runtime_disable(dev);
> > +       pm_runtime_set_active(dev);
> > +       pm_runtime_enable(dev);
> >         return 0;
> >  }
> >  #endif /* CONFIG_PM_SLEEP */
> >
> >
> > Thanks
> >
> > --
> > Qais Yousef
>
>