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

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Date:   Wed, 20 Jun 2018 12:15:00 +0300
From:   Mathias Nyman <mathias.nyman@...ux.intel.com>
To:     Peter Chen <peter.chen@....com>,
        Jia-Ju Bai <baijiaju1990@...il.com>,
        "mathias.nyman@...el.com" <mathias.nyman@...el.com>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
Cc:     "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [BUG] usb: xhci: Two possible sleep-in-atomic-context bugs

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