Re: musb RPM sleep-while-atomic in 4.9-rc1

[Johan Hovold <johan-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>]

On Tue, Oct 25, 2016 at 08:11:10AM -0700, Tony Lindgren wrote:
> * Johan Hovold <johan-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org> [161025 01:33]:
> > On Mon, Oct 24, 2016 at 10:35:38AM -0700, Tony Lindgren wrote:
> > 
> > > From: Tony Lindgren <tony-4v6yS6AI5VpBDgjK7y7TUQ@public.gmane.org>
> > > Date: Mon, 24 Oct 2016 09:18:02 -0700
> > > Subject: [PATCH] usb: musb: Fix sleeping function called from invalid
> > >  context for hdrc glue
> > > 
> > > Commit 65b3f50ed6fa ("usb: musb: Add PM runtime support for MUSB DSPS
> > > glue layer") wrongly added a call for pm_runtime_get_sync to otg_timer
> > > that runs in softirq context. That causes a "BUG: sleeping function called
> > > from invalid context" every time when polling the cable status:
> > > 
> > > [<c015ebb4>] (__might_sleep) from [<c0413d60>] (__pm_runtime_resume+0x9c/0xa0)
> > > [<c0413d60>] (__pm_runtime_resume) from [<c04d0bc4>] (otg_timer+0x3c/0x254)
> > > [<c04d0bc4>] (otg_timer) from [<c0191180>] (call_timer_fn+0xfc/0x41c)
> > > [<c0191180>] (call_timer_fn) from [<c01915c0>] (expire_timers+0x120/0x210)
> > > [<c01915c0>] (expire_timers) from [<c0191acc>] (run_timer_softirq+0xa4/0xdc)
> > > [<c0191acc>] (run_timer_softirq) from [<c010168c>] (__do_softirq+0x12c/0x594)
> > > 
> > > I did not notice that as I did not have CONFIG_DEBUG_ATOMIC_SLEEP enabled.
> > > 
> > > Let's fix the issue by adding dsps_check_status() and dsps_runtime_resume()
> > > functions. And let's have otg_timer() check for the PM runtime status, and
> > > if not already enabled, have dsps_runtime_resume() call dsps_check_status()
> > > directly.
> > 
> > While this makes the sleeping-while-atomic warning go away, it does not
> > seem correct. In case we were suspended, the glue layer will now call
> > dsps_check_status while the controller (child) is still suspended:
> > 
> > [    8.577538] musb-hdrc musb-hdrc.0.auto: otg_timer
> > [    8.582642] musb-dsps 47401400.usb: dsps_runtime_resume
> > [    8.600651] musb-hdrc musb-hdrc.0.auto: dsps_check_status
> > [    8.630617] musb-hdrc musb-hdrc.0.auto: musb_runtime_resume
> 
> Hmm that's a good point yeah. If we start doing something generic in
> musb-core.c musb_runtime_resume, things could go wrong in the future.
> 
> With this particular hardware musb registers are always accessible
> though when the parent of the two musb instances musb_am335x is done.
> 
> We could just reprogam the otg timer if !pm_runtime_active(dev). But
> the sucky things with that approach is that when idle we have two
> timers, one to wake-up, then another one to check the status.

Maybe add another callback from musb_runtime_resume that can be used for
such deferred work instead?

Johan
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