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Tue, 08 Jul 2025 11:16:50 -0700 (PDT) Received: from [192.168.1.14] ([38.175.170.29]) by smtp.gmail.com with ESMTPSA id 8926c6da1cb9f-503b5a29eb4sm2332522173.57.2025.07.08.11.16.49 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 08 Jul 2025 11:16:49 -0700 (PDT) Message-ID: <2a901b8a-9052-41d9-a70d-76508ebd819b@linuxfoundation.org> Date: Tue, 8 Jul 2025 12:16:48 -0600 Precedence: bulk X-Mailing-List: linux-usb@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] usbip: convert to use faux_device To: Zongmin Zhou , Greg KH Cc: shuah@kernel.org, valentina.manea.m@gmail.com, i@zenithal.me, linux-kernel@vger.kernel.org, linux-usb@vger.kernel.org, zhouzongmin@kylinos.cn, Shuah Khan References: <2a327b520760271471717fff9b222cdc34967489.1746662386.git.zhouzongmin@kylinos.cn> <20250604065410.76069-1-min_halo@163.com> <2025061926-paycheck-footnote-a2b8@gregkh> <2025062010-hardiness-flashily-cb0f@gregkh> <9d95bb75-586c-48dc-9e34-432cc13fd99f@163.com> <2025062004-navy-emboss-4743@gregkh> <2e0bbc5a-e74a-4fb5-884c-686dbaf99caf@linuxfoundation.org> <48ab511e-2847-4daa-98de-a234b8584b78@163.com> <1a13cf53-ffed-4521-917e-9c2856a5e348@linuxfoundation.org> <4fc877f0-b55b-4fa3-8df4-2de4ba1ac51b@163.com> Content-Language: en-US From: Shuah Khan In-Reply-To: <4fc877f0-b55b-4fa3-8df4-2de4ba1ac51b@163.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 7/3/25 00:04, Zongmin Zhou wrote: > > On 2025/7/3 07:54, Shuah Khan wrote: >> On 7/1/25 20:12, Zongmin Zhou wrote: >>> >>> On 2025/7/2 06:56, Shuah Khan wrote: >>>> On 6/23/25 21:21, Zongmin Zhou wrote: >>>>> >>>>> On 2025/6/21 01:26, Shuah Khan wrote: >>>>>> On 6/20/25 03:27, Greg KH wrote: >>>>>>> On Fri, Jun 20, 2025 at 05:19:33PM +0800, Zongmin Zhou wrote: >>>>>>>> >>>>>>>> On 2025/6/20 12:29, Greg KH wrote: >>>>>>>>> On Fri, Jun 20, 2025 at 10:16:16AM +0800, Zongmin Zhou wrote: >>>>>>>>>> On 2025/6/19 19:01, Greg KH wrote: >>>>>>>>>>> On Wed, Jun 04, 2025 at 02:54:10PM +0800, Zongmin Zhou wrote: >>>>>>>>>>>> From: Zongmin Zhou >>>>>>>>>>>> >>>>>>>>>>>> The vhci driver does not need to create a platform device, >>>>>>>>>>>> it only did so because it was simple to do that in order to >>>>>>>>>>>> get a place in sysfs to hang some device-specific attributes. >>>>>>>>>>>> Now the faux device interface is more appropriate,change it >>>>>>>>>>>> over to use the faux bus instead. >>>>>>>>>>>> >>>>>>>>>>>> Signed-off-by: Zongmin Zhou >>>>>>>>>>>> --- >>>>>>>>>>>> Changes in v2: >>>>>>>>>>>> - don't change faux create api,just call probe on vhci_hcd_init. >>>>>>>>>>>> >>>>>>>>>>>>     drivers/usb/usbip/vhci.h             |  4 +- >>>>>>>>>>>>     drivers/usb/usbip/vhci_hcd.c         | 86 +++++++++++----------------- >>>>>>>>>>>>     drivers/usb/usbip/vhci_sysfs.c       | 68 +++++++++++----------- >>>>>>>>>>>>     tools/usb/usbip/libsrc/vhci_driver.h |  2 +- >>>>>>>>>>>>     4 files changed, 72 insertions(+), 88 deletions(-) >>>>>>>>>>> I get the following build errors from this patch: >>>>>>>>>>> >>>>>>>>>>> drivers/usb/usbip/vhci_hcd.c:1462:12: error: ‘vhci_hcd_resume’ defined but not used [-Werror=unused-function] >>>>>>>>>>>     1462 | static int vhci_hcd_resume(struct faux_device *fdev) >>>>>>>>>>>          |            ^~~~~~~~~~~~~~~ >>>>>>>>>>> drivers/usb/usbip/vhci_hcd.c:1418:12: error: ‘vhci_hcd_suspend’ defined but not used [-Werror=unused-function] >>>>>>>>>>>     1418 | static int vhci_hcd_suspend(struct faux_device *fdev, pm_message_t state) >>>>>>>>>>>          |            ^~~~~~~~~~~~~~~~ >>>>>>>>>>> cc1: all warnings being treated as errors >>>>>>>>>>> >>>>>>>>>>> Are you sure you tested this? >>>>>>>>>> I apologize for not enabling -Werror, which resulted in missing this error >>>>>>>>>> warning. >>>>>>>>>> I have tested usbip feature use the new patch,but not test system >>>>>>>>>> suspend/resume. >>>>>>>>>> The faux bus type don't add pm function,and vhci-hcd driver can't register >>>>>>>>>> it. >>>>>>>>>> Maybe have to add suspend/resume for it.like below: >>>>>>>>>> static const struct bus_type faux_bus_type = { >>>>>>>>>>       .name        = "faux", >>>>>>>>>>       .match        = faux_match, >>>>>>>>>>       .probe        = faux_probe, >>>>>>>>>>       .remove        = faux_remove, >>>>>>>>>>       .resume     = faux_resume, >>>>>>>>>>       .suspend    = faux_suspend, >>>>>>>>>> }; >>>>>>>>>> >>>>>>>>>> Is that right? >>>>>>>>>> Your expertise would be greatly valued. >>>>>>>>> As this is not real hardware, why do you need the suspend/resume >>>>>>>>> callbacks at all?  What is happening here that requires them? >>>>>>>> @greg, >>>>>>>> The vhci_hcd_suspend/vhci_hcd_resume interfaces are not designed for this >>>>>>>> faux device, but rather to >>>>>>>> manipulate the HCD_FLAG_HW_ACCESSIBLE bit in the hcd flags associated with >>>>>>>> the faux device. >>>>>>>> For example: >>>>>>>> During system standby: clear_bit(HCD_FLAG_HW_ACCESSIBLE, &hcd->flags) >>>>>>>> During system wakeup: set_bit(HCD_FLAG_HW_ACCESSIBLE, &hcd->flags) >>>>>>>> >>>>>>>> Previously, these two functions were registered through platform_driver, >>>>>>>> but faux bus does not have the relevant interface, so they were not called, >>>>>>>> resulting in this compilation warning error. >>>>>>>> >>>>>>>> This raises the question: Should the faux bus implement PM-related >>>>>>>> interface? >>>>>>>> I'm uncertain whether these functions are essential for the vhci-hcd driver >>>>>>>> or if they can be safely removed. >>>>>>>> >>>>>>>> However, during system standby/wakeup tests with remote USB devices bound to >>>>>>>> the vhci-hcd driver, >>>>>>>> I observed consistent failure scenarios across both the original platform >>>>>>>> bus and faux bus patch implementations. >>>>>> >>>>>> suspend and resume hooks have been in the code from beginning >>>>>> in the CONFIG_PM path. The original authors are skeptical about >>>>>> what should happen during suspend" >>>>>> >>>>>> /* what should happen for USB/IP under suspend/resume? */ >>>>>> suspend hook checks for active connections and sends EBBUSY >>>>>> back to pm core. >>>>>> >>>>>> Active connection means any of the ports are in USB_PORT_STAT_CONNECTION >>>>>> state. So as long as there are active connections between vhci client >>>>>> and the host, suspend won't work. So we really don't know what happens >>>>>> to the active connections if there are no suspend/resume hooks. >>>>>> >>>>>> If there are no active connections, then it will clear the HCD_FLAG_HW_ACCESSIBLE >>>>>> bit and returns to pm core to continue with suspend. >>>>>> >>>>>> resume sets the HCD_FLAG_HW_ACCESSIBLE flag to indicate hardware is accessible >>>>>> and initiates port status poll. >>>>>> >>>>>> - suspend hook prevents suspend >>>>>> >>>>>> With faux device since there is no suspend and resume hook, I would expect >>>>>> these hooks are not a factor in suspend and resume. >>>>>> >>>>>> vhci_hcd is a special case virtual driver as it is a proxy for controlling >>>>>> hardware on the host. >>>>>> >>>>>> Zongmin, >>>>>> >>>>>> Do suspend/resume work when vhci_hcd is not loaded? >>>>>> What happens when when system suspends and resumes with faux device? >>>>>> Can you send me dmesg logs and pm logs? >>>>>> >>>>> Hi Greg,shuah >>>>> >>>>> Yes, system with vhci_hcd unload or just load vhci_hcd driver >>>>> without usbip devices bound to vhci_hcd,system suspend/resume worked well. >>>>> Some logs for you. >>>> >>>> Sorry for the delay. I was at a conference last week. >>>> Thank you for sending these logs. >>>> >>>>> 1.system with vhci_hcd driver load,but don't bound any usbip devices to vhci_hcd,suspend/resume worked well. >>>>> see dmesg-faux bus-load.log >>>> >>>> >>>>> >>>>> 2.usbip device bound to vhci_hcd,and do system suspend action,suspend/resume worked failed. >>>>> I observed two distinct failure scenario: >>>>> Scenario 1: System failed to enter suspend state,and will auto resume; >>>> >>>> >>>>> the log for use platform bus: >>>>> dmesg-platform bus-device bound-auto resume.log >>>> >>>> This is clear from the suspend hook in the vhci_hcd. >>>> When it returns EBUSY, suspend will fail and move to >>>> auto resume. >>>> >>>>> the log for use faux bus: >>>>> dmesg-faux bus-device bound-auto resume.log >>>> >>>> It is good that the behavior is same with faux bus even though >>>> suspend hook isn't called. I will take a look at the log. >>>> >>>>> >>>>> Scenario 2: System resume failed with black screen freeze,a forced restart of the machine is require. >>>>> the log for use platform bus: >>>>> dmesg-platform bus-device bound-black screen.log >>>>> the log for use faux bus: >>>>> dmesg-faux bus-device bound-black screen.log >>>> >>>> That is bad. When does this happen? Is there a difference in >>>> configuration? >>>> >>> No, there's no difference. The same code is used for two different failure scenarios. >>> I just tested many times. These two different situations occur probabilistically. >>> But they both happened only when the USBIP device is bound to the vhci_hcd driver. >>>> The behavior same for platform bus and faux bus. Sounds like >>>> an existing problem that needs to be debugged separately. >>>> >>>> I will take a look at all these logs and get back to you in >>>> a day or two. >>>> >> >> I looked at the logs and here is what I found: >> >> Scenario 1: >>   dmesg-faux bus-device bound-auto resume.log >>   dmesg-platform bus-device bound-auto resume.log >> >> In this case suspend bailed out way before driver suspend >> when vhci_hcd is using platform and faux bus. >> >> Freezing remaining freezable tasks failed after 20.006 seconds (0 tasks refusing to freeze, wq_busy=1) >> Restarting kernel threads ... done >> OOM killer enabled. >> Restarting tasks ... done. >> random: crng reseeded on system resumption >> PM: suspend exit >> >> Auto-resume of the user-space worked. Scenario 1 isn't really >> interesting. >> >> Scenario 2: >>   dmesg-faux bus-device bound-black screen.log >>   dmesg-platform bus-device bound-black screen.log >> >> Even though the result is the same in seeing blank screen, how >> we get there is different. >> >> ================= >> faux-bus device: >> ================= >> - suspend worked - looks like >>   usb 4-1: PM: calling usb_dev_suspend @ 6054, parent: usb4 >>   usb 4-1: PM: usb_dev_suspend returned 0 after 13675 usecs >>   usb usb4: PM: calling usb_dev_suspend @ 6055, parent: vhci_hcd.0 >>   usb usb4: PM: usb_dev_suspend returned 0 after 9 usecs >> >> vhci_hcd suspend isn't in play here. usb_dev_suspend() returns. >> See below >> >> usb 4-1: PM: usb_dev_suspend returned message. >> >> ------------------------------------------------------------- >> >> - resume started (assuming it has been initiated by user) >> >> [  650.027491][ T6056] pci 0000:00:01.0: PM: pci_pm_suspend_noirq returned 0 after 304 usecs >> >> See see timestamp difference between the last suspend message and the >> first resume message. >> [  674.000257][   T39] pci 0000:00:00.0: PM: calling pci_pm_resume_noirq @ 39, parent: pci0000:00 >> >> usb 4-1 usb_dev_resume never returns. >> >> [  674.071125][ T6117] usb usb4: PM: usb_dev_resume returned 0 after 21110 usecs >> [  674.113991][ T6126] usb 4-1: PM: calling usb_dev_resume @ 6126, parent: usb4 >> >> ------------------------------------------------------------- >> >> ===================== >> platform bus device >> ===================== >> >> - suspend was aborted because vhci_hcd suspend routine returned error >> >> [  297.854621][ T9402] usb 4-1: PM: calling usb_dev_suspend @ 9402, parent: usb4 >> [  297.868524][ T9402] usb 4-1: PM: usb_dev_suspend returned 0 after 13214 usecs >> [  297.869994][ T9403] usb usb4: PM: calling usb_dev_suspend @ 9403, parent: vhci_hcd.0 >> [  297.871959][ T9403] usb usb4: PM: usb_dev_suspend returned 0 after 30 usecs >> [  297.873644][ T9394] vhci_hcd vhci_hcd.0: PM: calling platform_pm_suspend @ 9394, parent: platform >> [  297.874738][ T9394] vhci_hcd vhci_hcd.0: We have 1 active connection. Do not suspend. >> [  297.875369][ T9394] vhci_hcd vhci_hcd.0: PM: dpm_run_callback(): platform_pm_suspend returns -16 >> [  297.876078][ T9394] vhci_hcd vhci_hcd.0: PM: platform_pm_suspend returned -16 after 1341 usecs >> [  297.876774][ T9394] vhci_hcd vhci_hcd.0: PM: failed to suspend: error -16 >> >> - the following triggers resume >> [  297.877321][ T9394] PM: Some devices failed to suspend, or early wake event detected >> >> [  297.881065][ T9403] usb usb3: PM: usb_dev_resume returned 0 after 19 usecs >> [  297.904551][ T9408] usb usb4: PM: usb_dev_resume returned 0 after 22911 usecs >> [  297.905148][ T9418] usb 4-1: PM: calling usb_dev_resume @ 9418, parent: usb4 >> >> usb 4-1 usb_dev_resume never returns. >> >> Note - In both cases, usb_dev_resume doesn't return. When it is called is the >> difference. >> >> I don't think suspend/resume works when devices are bound. Suspend exits and >> starts resume which seems to fail because it doesn't handle the virtual usb >> device resume. There is a missing piece here. >> >> When vhci_hcd imports a device and acts as a proxy between the virtual mass >> storage device (e.g in this case) - it appears suspend and resume are >> handled as if it is a usb device. Maybe this is incorrect? >> >> usb_dev_suspend() works and usb_dev_resume() on these virtual usb devices? >> Do we need to handle this in usb_dev_resume()? >> >> Talking out loud - I have to do some looking into. >> > Re: > Yes, your analysis is completely correct. > > In fact, I've experimented with adding PM hooks to the faux bus, > and found that faux bus devices then behave identically to platform bus devices during suspend/resume. > See the attachment. > Thanks for checking this scenario. No surprises here. > This is likely a historical legacy issue. It is an existing problem in the way vhci_hcd and the bound devices handle suspend/resume. vhci_hcd suspend assumes once it returns "don't suspend" the rest works. However suspend for the bound device runs first and a subsequent resume on it fails. This problem needs fixing - I don't know yet how to. > Regarding this matter, is there anything else you'd like me to assist with? > One thing I am curious about is the status of the bound devices after "forced restart of the machine" when you see blank screen or hang? thanks, -- Shuah