linux-kernel - Re: [PATCH v2 01/18] usb: vhci-hcd: Prevent suspending virtually attached devices

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Message-ID: <c7c76b11-f7db-4cfd-81ac-c43d8c540472@collabora.com>
Date: Mon, 28 Jul 2025 13:03:43 +0300
From: Cristian Ciocaltea <cristian.ciocaltea@...labora.com>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Valentina Manea <valentina.manea.m@...il.com>,
 Shuah Khan <shuah@...nel.org>, Hongren Zheng <i@...ithal.me>,
 "Brian G. Merrell" <bgmerrell@...ell.com>, kernel@...labora.com,
 Greg Kroah-Hartman <gregkh@...e.de>, linux-usb@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 01/18] usb: vhci-hcd: Prevent suspending virtually
 attached devices

On 7/26/25 10:06 AM, Greg Kroah-Hartman wrote:
> On Sat, Jul 26, 2025 at 01:08:03AM +0300, Cristian Ciocaltea wrote:
>> The VHCI platform driver aims to forbid entering system suspend when at
>> least one of the virtual USB ports are bound to an active USB/IP
>> connection.
>>
>> However, in some cases, the detection logic doesn't work reliably, i.e.
>> when all devices attached to the virtual root hub have been already
>> suspended, leading to a broken suspend state, with unrecoverable resume.
>>
>> Ensure the virtually attached devices do not enter suspend by setting
>> the syscore PM flag.  Note this is currently limited to the client side
>> only, since the server side doesn't implement system suspend prevention.
>>
>> Fixes: 04679b3489e0 ("Staging: USB/IP: add client driver")
>> Signed-off-by: Cristian Ciocaltea <cristian.ciocaltea@...labora.com>
>> ---
>>  drivers/usb/usbip/vhci_hcd.c | 22 ++++++++++++++++++++++
>>  1 file changed, 22 insertions(+)
>>
>> diff --git a/drivers/usb/usbip/vhci_hcd.c b/drivers/usb/usbip/vhci_hcd.c
>> index e70fba9f55d6a0edf3c5fde56a614dd3799406a1..b4b0ed5d64966214636b157968478600e2e4178a 100644
>> --- a/drivers/usb/usbip/vhci_hcd.c
>> +++ b/drivers/usb/usbip/vhci_hcd.c
>> @@ -765,6 +765,17 @@ static int vhci_urb_enqueue(struct usb_hcd *hcd, struct urb *urb, gfp_t mem_flag
>>  				 ctrlreq->wValue, vdev->rhport);
>>  
>>  			vdev->udev = usb_get_dev(urb->dev);
>> +			/*
>> +			 * FIXME: A similar operation has been done via
>> +			 * USB_REQ_GET_DESCRIPTOR handler below, which is
>> +			 * supposed to always precede USB_REQ_SET_ADDRESS.
> 
> When is this FIXME going to be addressed and by whom?

Actually I should have probably used a NOTE or something similar as this is
only about the possibility to drop some redundant code, rather then fixing
something broken.

>> +			 *
>> +			 * It's not entirely clear if operating on a different
>> +			 * usb_device instance here is a real possibility,
>> +			 * otherwise this call and vdev->udev assignment above
>> +			 * should be dropped.
> 
> What is going to need to happen to figure this out?

I could only do some limited testing on my side, which is definitely not
enough to confirm it's safe to move on with the code removal, hence I'd very
much like to get some other opinions on the matter.  Regardless, I think
it's useful to keep this documented.

Thanks,
Cristian