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

    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.

    Alan Stern

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