linux-kernel - Re: [PATCH] USB: Fix the issue of task recovery failure caused by USB status when S4 wakes up

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Message-ID: <8068130ce4ece6078b2893c4c6333c06c792b6c0.camel@kylinos.cn>
Date: Thu, 12 Sep 2024 11:21:26 +0800
From: duanchenghao <duanchenghao@...inos.cn>
To: Alan Stern <stern@...land.harvard.edu>
Cc: gregkh@...uxfoundation.org, pavel@....cz, linux-pm@...r.kernel.org, 
	niko.mauno@...sala.com, stanley_chang@...ltek.com, tj@...nel.org, 
	linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org
Subject: Re: [PATCH] USB: Fix the issue of task recovery failure caused by
 USB status when S4 wakes up

在 2024-09-11星期三的 10:40 -0400，Alan Stern写道：
> On Tue, Sep 10, 2024 at 05:36:56PM +0800, duanchenghao wrote:
> > S4 wakeup restores the image that was saved before the system
> > entered
> > the S4 sleep state.
> > 
> >     S4 waking up from hibernation
> >     =============================
> >     kernel initialization
> >     |   
> >     v   
> >     freeze user task and kernel thread
> >     |   
> >     v   
> >     load saved image
> >     |    
> >     v   
> >     freeze the peripheral device and controller
> >     (Check the HCD_FLAG_WAKEUP_ PENDING flag of the USB. If it is
> > set,
> >      return to EBUSY and do not perform the following restore
> > image.)
> 
> Why is the flag set at this point?  It should not be; the device and 
> controller should have been frozen with wakeup disabled.
> 
This is check point, not set point. When the USB goes into a suspend
state, the HCD_FLAG_WAKEUP_PENDING flag is checked, and if it is found
that the USB is in the process of resuming, then an EBUSY error is
returned.

> >     |
> >     v
> >     restore image(task recovery)
> 
> > > > However, upon detecting that the hcd is in the
> > > > HCD_FLAG_WAKEUP_PENDING state,
> > > > it will return an EBUSY status, causing the S4 suspend to fail
> > > > and
> > > > subsequent task recovery to not proceed.
> > > 
> > > What will return an EBUSY status?
> > 
> > if HCD_FLAG_WAKEUP_PENDING flag is set_bit, will return EBUSY.
> 
> I meant: Which function will return EBUSY status?  The answer is in
> the 
> log below; hcd_pci_suspend() does this.
> 
> > > Why do you say that S4 suspend will fail?  Aren't you talking
> > > about
> > > S4 
> > > wakeup?
> > 
> > After returning EBUSY, the subsequent restore image operation will
> > not
> > be executed.
> > 
> > > 
> > > Can you provide a kernel log that explains these points and shows
> > > what 
> > > problem you are trying to solve?
> > 
> > [    9.009166][ 2] [  T403] PM: Image signature found, resuming
> > [    9.009167][ 2] [  T403] PM: resume from hibernation
> > [    9.009243][ 2] [  T403] inno-codec inno-codec.16.auto:
> > [inno_vpu][vpu_notifier:1540]vpu_notifier: untested action 5...
> > [    9.009244][ 2] [  T403] Freezing user space processes ...
> > (elapsed
> > 0.001 seconds) done.
> > [    9.010355][ 2] [  T403] OOM killer disabled.
> > [    9.010355][ 2] [  T403] Freezing remaining freezable tasks ...
> > (elapsed 0.000 seconds) done.
> > [    9.012152][ 2] [  T403] PM: Basic memory bitmaps created
> > [    9.073333][ 2] [  T403] PM: Using 3 thread(s) for decompression
> > [    9.073334][ 2] [  T403] PM: Loading and decompressing image
> > data
> > (486874 pages)...
> > [    9.073335][ 2] [  T403] hibernate: Hibernated on CPU 0
> > [mpidr:0x0]
> > [    9.095928][ 2] [  T403] PM: Image loading progress:   0%
> > [    9.664803][ 2] [  T403] PM: Image loading progress:  10%
> > [    9.794156][ 2] [  T403] PM: Image loading progress:  20%
> > [    9.913001][ 2] [  T403] PM: Image loading progress:  30%
> > [   10.034331][ 2] [  T403] PM: Image loading progress:  40%
> > [   10.154070][ 2] [  T403] PM: Image loading progress:  50%
> > [   10.277096][ 2] [  T403] PM: Image loading progress:  60%
> > [   10.398860][ 2] [  T403] PM: Image loading progress:  70%
> > [   10.533760][ 2] [  T403] PM: Image loading progress:  80%
> > [   10.659874][ 2] [  T403] PM: Image loading progress:  90%
> > [   10.760681][ 2] [  T403] PM: Image loading progress: 100%
> > [   10.760693][ 2] [  T403] PM: Image loading done
> > [   10.760718][ 2] [  T403] PM: Read 1947496 kbytes in 1.68 seconds
> > (1159.22 MB/s)
> > [   10.761982][ 2] [  T403] PM: Image successfully loaded
> > [   10.761988][ 2] [  T403] printk: Suspending console(s) (use
> > no_console_suspend to debug)
> > [   10.864973][ 2] [  T403] innovpu_freeze:1782
> > [   10.864974][ 2] [  T403] innovpu_suspend:1759
> > [   11.168871][ 2] [  T189] PM: pci_pm_freeze():
> > hcd_pci_suspend+0x0/0x38 returns -16
> 
> This should not be allowed to happen.  Freezing is mandatory and not 
> subject to wakeup requests.
> 
> Is your problem related to the one discussed in this email thread?
> 
> https://lore.kernel.org/linux-usb/d8600868-6e4b-45ab-b328-852b6ac8ecb5@rowland.harvard.edu/
> 
> Would the suggestion I made there -- i.e., have the xhci-hcd 
> interrupt handler skip calling usb_hcd_resume_root_hub() if the root
> hub 
> was suspended with wakeup = 0 -- fix your problem?

Skipping usb_hcd_resume_root_hub() should generally be possible, but
it's important to ensure that normal remote wakeup functionality is not
compromised. Is it HUB_SUSPEND that the hub you are referring to is in
a suspended state?

v2 patch:
https://lore.kernel.org/all/20240910105714.148976-1-duanchenghao@kylinos.cn/
> 
> Alan Stern