On Wed, Sep 25, 2024 at 10:50:41AM +0800, dengjie wrote:
> Reproduction of the problem: During the S4 stress test, when a USB device is inserted or
> removed, there is a probability that the S4 wakeup will turn into a reboot.The following
> two points describe how to analyze and locate the problem points:
>
> 1. During the boot stage when S4 is awakened, after the USB RootHub is initialized,
> it will enter the runtime suspend state. From then on, whenever an xhci port change
> event occurs, it will trigger a remote wakeup request event and add wakeup_work
> to pm_wq, where the subsequent RootHub runtime resume process will be handled by pm_wq.
>
> xhci runtime suspend flow：
> S4 boot
> |->xhci init
> |->register_root_hub
> |->hub_probe
> |->callback = RPM_GET_CALLBACK(dev, runtime_suspend) /* xhci RootHub runtime suspend */
>
> xhci runtime resume flow ：
> xhci_irq()
> |->xhci_handle_event()
> |->handle_port_status()
> |->if(hcd->state == HC_STATE_SUSPENDED)
> |->usb_hcd_resume_root_hub()
> |->set_bit(HCD_FLAG_WAKEUP_PENDING, &hcd->flags) /* wakeup pending signal to be set */
> |->queue_work(pm_wq, &hcd->wakeup_work)
> |->hcd_resume_work() /* hcd->wakeup_work */
> |->usb_remote_wakeup()
> |->callback = RPM_GET_CALLBACK(dev, runtime_resume)
> |->usb_runtime_resume() /* usb runtime resume */
> |->generic_resume()
> |->hcd_bus_resume()
> |->clear_bit(HCD_FLAG_WAKEUP_PENDING, &hcd->flags);
> /* wakeup pending signal to be clear */
>
> 2. However, during the quiesce phase of S4 wakeup, freeze_kernel_threads() will freeze this pm_wq,
> and between freeze_kernel_threads() and dpm_suspend_start(), there exists a very time-consuming
> S4 image loading process. This leads to a situation where, if an xhci port change event occurs
> after freeze_kernel_threads(), triggering the wakeup pending signal to be set,but it cannot
> be processed by pm_wq to clear this wakeup_pending bit, it will result in a subsequent
> dpm_suspend_start() where USB suspend_common() detects the wakeup pending signal being
> set and returns an -EBUSY error, interrupting the S4 quiesce process and reverting to a reboot.
>
> S4 wakeup
> |->resume_store
> |->software_resume()
> |->freeze_kernel_threads() /* will freeze pm_wq */
> |->load_image_and_restore()
> |->swsusp_read() /* S4 image loading: time-consuming .
> When an xhci port change event occurs at this point, it triggers the wakeup pending signal to be set.
> However, since the pm_wq is in a frozen state, the wakeup_pending bit cannot be cleared.*/
> |->hibernation_restore
> |->dpm_suspend_start(PMSG_QUIESCE)
> |->hcd_pci_suspend()
> |->suspend_common()
> |->if (do_wakeup && HCD_WAKEUP_PENDING(hcd)) return -EBUSY;
>
> Below is a description of the countermeasures taken to address this issue:
> 1. Considering the restore process that occurs after the quiesce phase during S4 wakeup,
> which essentially resets all root hubs,checking this wakeup pending status in USB suspend_common()
> during the quiesce phase is of little significance and should therefore be filtered out.
>
> S4 wakeup restore phase
> |->dpm_resume(PMSG_RESTORE)
> |->hcd_pci_restore()
> |->xhci_resume() /* reset all root hubs */
>
> Fixes: 3904bdf0821c ("PM: hibernate: Freeze kernel threads in software_resume()")
> Signed-off-by: dengjie <dengjie03@xxxxxxxxxx>
What happened to the other authorship information?
And again, please use your name, not an email alias.
thanks,
greg k-h
