Re: [linux-pm] Resume hangs [was: mmotm 2010-12-02-16-34 uploaded]

[Rafael J. Wysocki]

On Wednesday, March 30, 2011, Alan Stern wrote:
> On Wed, 30 Mar 2011, Jiri Slaby wrote:
> 
> > > Strange indeed.  It's worth noting that the async stuff affects only
> > > the normal suspend and resume operations, not the late-suspend and
> > > early-resume operations.  This means that it all likelihood, the system
> > > crashes either before finishing the suspend or after doing a fair
> > > amount of the resume.  And yet that's not consistent with what you see
> > > on the screen.
> > > 
> > > By the way, are you booting with no_console_suspend?  And do you do 
> > > "echo 8 >/proc/sys/kernel/printk" (or equivalently, Alt-SysRq-8) before 
> > > suspending?
> > 
> > I'm testing this on my desktop. I found out yesterday, that I had async
> > completely disabled. So I have no output yet.
> > 
> > I took my dvb-t tuner from desktop and connected it to my notebook. And
> > got a similar hang during resume right now. It may not be related
> > though. The trace is:
> > s2disk          D 0000000000000000     0  6125   5902 0x00000004
> >  ffff8800797aba78 0000000000000082 ffff8800797ab9f8 0000000000012ac0
> >  ffff8800797abfd8 0000000000012ac0 ffff8800797abfd8 ffff8800797abfd8
> >  ffff8800777fe7f0 0000000000012ac0 0000000000012ac0 ffff8800797aa000
> > Call Trace:
> >  [<ffffffff8151e2ed>] schedule_timeout+0x28d/0x310
> >  [<ffffffff8151d410>] wait_for_common+0xc0/0x150
> >  [<ffffffff8133ad22>] _request_firmware+0x132/0x270
> >  [<ffffffffa06df2c7>] dvb_usb_download_firmware+0x37/0xf0 [dvb_usb]
> >  [<ffffffffa06dfbe5>] dvb_usb_device_init+0x165/0x1b0 [dvb_usb]
> >  [<ffffffffa06d6c27>] af9015_usb_probe+0x87/0xa0 [dvb_usb_af9015]
> >  [<ffffffff8138d9d2>] usb_probe_interface+0x142/0x270
> >  [<ffffffff8132f3c0>] really_probe+0x70/0x220
> >  [<ffffffff8132f757>] driver_probe_device+0x47/0xa0
> >  [<ffffffff8132e19c>] bus_for_each_drv+0x5c/0x90
> >  [<ffffffff8132f62f>] device_attach+0x8f/0xb0
> >  [<ffffffff8138d5b0>] usb_rebind_intf+0x60/0xa0
> >  [<ffffffff8138d6c7>] do_unbind_rebind+0x77/0xb0
> >  [<ffffffff8138d76b>] usb_resume+0x6b/0xb0
> >  [<ffffffff8137f96b>] usb_dev_complete+0xb/0x10
> >  [<ffffffff81334d1e>] device_complete+0x8e/0xe0
> >  [<ffffffff81335da1>] dpm_resume_end+0xa1/0x120
> >  [<ffffffff8109d890>] hibernation_snapshot+0xc0/0x120
> >  [<ffffffff810a1cde>] snapshot_ioctl+0x3ae/0x590
> >  [<ffffffff81169794>] do_vfs_ioctl+0x84/0x2f0
> >  [<ffffffff81169a98>] sys_ioctl+0x98/0xa0
> >  [<ffffffff81002ed2>] system_call_fastpath+0x16/0x1b
> >  [<00007fe6c82f8ce7>] 0x7fe6c82f8ce7
> > 
> > 
> > The firmware request should time out. I think I waited for longer than
> > 60 s before when I saw the hangs on the desktop, But do you have an idea
> > why it doesn't load the FW immediately?
> 
> I don't know why the request didn't time out, but this behavior should
> at least be reproducible.  Your stack trace implies that the firmware
> will need to be transferred every time the device resumes... but of
> course this leaves open the question of why your desktop crashed only
> occasionally.
> 
> Probably the firmware wasn't transferred immediately because the kernel
> relies on a userspace process to find and load the firmware, but at
> that point userspace was still frozen.
> 
> Rafael, this does seem to be a general problem.  Suppose a new device
> gets connected while the system is suspended.  How is the driver's
> probe method supposed to cope if it gets called while userspace is
> still frozen but it needs to load some firmware?
> 
> Is the answer that probing should always be delayed until after tasks
> are thawed?  There must be lots of subsystems which would have trouble 
> doing that, although we ought to be able to implement delayed probing 
> from within the driver core easily enough.

I don't know how to solve that.

First off, the prepare routines of drivers that need to load firmware during
resume probably should preload the firmware for the devices present during the
suspend.

Second, I don't generally think drivers should probe for devices during resume.
I guess the delayed probing would be the cleanest appoach here.

Thanks,
Rafael
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