Re: [BUG] usb: xhci: Two possible sleep-in-atomic-context bugs

[Mathias Nyman]

On 20.06.2018 06:28, Peter Chen wrote:
>   
> > The driver may sleep with holding a spinlock.
> > The function call paths (from bottom to top) in Linux-4.16.7 are:
> >
> > [FUNC] schedule
> > drivers/base/power/runtime.c, 741: schedule in rpm_resume
> > drivers/base/power/runtime.c, 1322: rpm_resume in pm_runtime_forbid
> > drivers/usb/host/xhci-hub.c, 647: pm_runtime_forbid in xhci_enter_test_mode
> > drivers/usb/host/xhci-hub.c, 632: _raw_spin_lock_irqsave in xhci_enter_test_mode
> >
> > [FUNC] schedule
> > drivers/base/power/runtime.c, 570: schedule in rpm_suspend
> > drivers/base/power/runtime.c, 434: rpm_suspend in rpm_idle
> > drivers/base/power/runtime.c, 1343: rpm_idle in pm_runtime_allow
> > drivers/usb/host/xhci-hub.c, 670: pm_runtime_allow in xhci_exit_test_mode
> > drivers/usb/host/xhci-hub.c, 1387: xhci_exit_test_mode in xhci_hub_control
> > drivers/usb/host/xhci-hub.c, 1038: _raw_spin_lock_irqsave in xhci_hub_control
> >
> > These bugs are found by my static analysis tool (DSAC-2) and checked by my code
> > review.
>
> I don't think runtime PM API is needed at xhci_hub_control since the controller should
> be always active, Mathias, do you agree I delete pm_runtime_forbid and pm_runtime_allow
> to fix this issue?

The USB2 test mode is a bit special, it will disable all connected devices, and halt the host.
Port should stay in test mode until feature is cleared or host reset.
There is a risk runtime suspend will try to suspend the host as no devices seem preset.

But I think pm_runtime_get_noresume() and pm_runtime_put_noidle() could be used instad,
those should be safe.

-Mathias