linux-kernel - Re: [PATCH v2] USB: Fix the issue of S4 wakeup queisce phase where task resumption fails due to USB status

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Message-ID: <2024092543-enforcer-quaintly-9f3e@gregkh>
Date: Wed, 25 Sep 2024 08:40:10 +0200
From: Greg KH <gregkh@...uxfoundation.org>
To: dengjie <dengjie03@...inos.cn>
Cc: rafael@...nel.org, pavel@....cz, len.brown@...el.com,
	linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-pm@...r.kernel.org, xiehongyu1@...inos.cn,
	duanchenghao@...inos.cn, xiongxin@...inos.cn
Subject: Re: [PATCH v2] USB: Fix the issue of S4 wakeup queisce phase where
 task resumption fails due to USB status

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@...inos.cn>

What happened to the other authorship information?

And again, please use your name, not an email alias.

thanks,

greg k-h