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SubjectRe: PCI / PM: Crashes in PME scan during system suspend
Hi Lukas,

On Sun, Apr 16, 2017 at 9:55 AM, Lukas Wunner <lukas@wunner.de> wrote:
> On Sat, Apr 15, 2017 at 12:27:31AM +0200, Rafael J. Wysocki wrote:
>> On Friday, April 14, 2017 10:22:49 AM Lukas Wunner wrote:
>> > Below is a tentative patch which moves PME polling to a freezable
>> > workqueue, so it is frozen before the host bridge is suspended.
>> > Geert, Laurent, could you test this?
>> >
>> > The patch may be problematic in that pci_pme_list_scan() acquires
>> > pci_pme_list_mutex, which is also acquired by pci_pme_active(),
>> > which gets called when devices are suspended -- *after* the worker
>> > has been frozen. I'm not really familiar with the freezer, can it
>> > happen that the worker is frozen while holding the mutex? If so
>> > this would deadlock. Rafael?
>>
>> That depends on the worker, precisely on where it calls try_to_freeze().
>
> pci_pme_list_scan() doesn't call try_to_freeze() at all, that's what had
> me confused. Neither do many other workers that are scheduled to
> system_freezable_wq.
>
> However after familiarizing myself a bit more with the freezer it seems
> that is fine. The freezer prevents new workers from being scheduled and
> then schedules the existing workers for up to 20 seconds to allow them
> to finish. The call to try_to_freeze() is thus only needed for long
> running workers or for threads which are in some infinite loop.
>
> Below is the same patch with a proper commit message, it's mostly copied
> and pasted from Geert's comprehensive report. Still needs to be tested
> by Geert and/or Laurent as I was unable reproduce the issue on my x86
> laptop. Perhaps on x86 the OS is not responsible for disabling the PCI
> clock (but presumably the BIOS) or x86 doesn't emit this kind of fault.

Thanks, works fine (see below)!

> -- >8 --
> Subject: [PATCH] PCI: Freeze PME scan before suspending devices
>
> Laurent Pinchart reported that the Renesas R-Car H2 Lager board
> (r8a7790) crashes during suspend tests. Geert Uytterhoeven managed to
> reproduce the issue on an M2-W Koelsch board (r8a7791):
>
> It occurs when the PME scan runs, once per second. During PME scan, the
> PCI host bridge (rcar-pci) registers are accessed while its module clock
> has already been disabled, leading to the crash.
>
> The issue only occurs during suspend tests, after writing either
> "platform" or "processors" to /sys/power/pm_test. It does not (or is
> less likely) to happen during full system suspend ("core" or "none")
> because system suspend also disables timers, and thus the workqueue
> handling PME scans no longer runs. Geert believes the issue may still
> happen in the small window between disabling module clocks and disabling
> timers.

It can also be reproduced easily by configuring s2ram to use s2idle instead
of deep suspend, which is a real usecase:

# echo 0 > /sys/module/printk/parameters/console_suspend
# echo s2idle > /sys/power/mem_sleep
# echo mem > /sys/power/state

> Rafael Wysocki agrees that PME scans should be suspended before the host
> bridge registers become inaccessible. To that end, queue the task on a
> workqueue that gets frozen before devices suspend.
>
> How to reproduce:
>
> # echo 0 > /sys/module/printk/parameters/console_suspend
> # echo platform > /sys/power/pm_test # Or "processors"
> # echo mem > /sys/power/state
>
> Make sure CONFIG_PCI_RCAR_GEN2 and CONFIG_USB_OHCI_HCD_PCI are
> enabled.
>
> PM: Syncing filesystems ... [ 38.566237] done.
> PM: Preparing system for sleep (mem)
> Freezing user space processes ... [ 38.579813] (elapsed 0.001 seconds) done.
> Freezing remaining freezable tasks ... (elapsed 0.001 seconds) done.
> PM: Suspending system (mem)
> PM: suspend of devices complete after 152.456 msecs
> PM: late suspend of devices complete after 2.809 msecs
> PM: noirq suspend of devices complete after 29.863 msecs
> suspend debug: Waiting for 5 second(s).
> Unhandled fault: asynchronous external abort (0x1211) at 0x00000000
> pgd = c0003000
> [00000000] *pgd=80000040004003, *pmd=00000000
> Internal error: : 1211 [#1] SMP ARM
> Modules linked in:
> CPU: 1 PID: 20 Comm: kworker/1:1 Not tainted
> 4.9.0-rc1-koelsch-00011-g68db9bc814362e7f #3383
> Hardware name: Generic R8A7791 (Flattened Device Tree)
> Workqueue: events pci_pme_list_scan
> task: eb56e140 task.stack: eb58e000
> PC is at pci_generic_config_read+0x64/0x6c
> LR is at rcar_pci_cfg_base+0x64/0x84
> pc : [<c041d7b4>] lr : [<c04309a0>] psr: 600d0093
> sp : eb58fe98 ip : c041d750 fp : 00000008
> r10: c0e2283c r9 : 00000000 r8 : 600d0013
> r7 : 00000008 r6 : eb58fed6 r5 : 00000002 r4 : eb58feb4
> r3 : 00000000 r2 : 00000044 r1 : 00000008 r0 : 00000000
> Flags: nZCv IRQs off FIQs on Mode SVC_32 ISA ARM Segment user
> Control: 30c5387d Table: 6a9f6c80 DAC: 55555555
> Process kworker/1:1 (pid: 20, stack limit = 0xeb58e210)
> Stack: (0xeb58fe98 to 0xeb590000)
> fe80: 00000002 00000044
> fea0: eb6f5800 c041d9b0 eb58feb4 00000008 00000044 00000000 eb78a000 eb78a000
> fec0: 00000044 00000000 eb9aff00 c0424bf0 eb78a000 00000000 eb78a000 c0e22830
> fee0: ea8a6fc0 c0424c5c eaae79c0 c0424ce0 eb55f380 c0e22838 eb9a9800 c0235fbc
> ff00: eb55f380 c0e22838 eb55f380 eb9a9800 eb9a9800 eb58e000 eb9a9824 c0e02100
> ff20: eb55f398 c02366c4 eb56e140 eb5631c0 00000000 eb55f380 c023641c 00000000
> ff40: 00000000 00000000 00000000 c023a928 cd105598 00000000 40506a34 eb55f380
> ff60: 00000000 00000000 dead4ead ffffffff ffffffff eb58ff74 eb58ff74 00000000
> ff80: 00000000 dead4ead ffffffff ffffffff eb58ff90 eb58ff90 eb58ffac eb5631c0
> ffa0: c023a844 00000000 00000000 c0206d68 00000000 00000000 00000000 00000000
> ffc0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
> ffe0: 00000000 00000000 00000000 00000000 00000013 00000000 3a81336c 10ccd1dd
> [<c041d7b4>] (pci_generic_config_read) from [<c041d9b0>]
> (pci_bus_read_config_word+0x58/0x80)
> [<c041d9b0>] (pci_bus_read_config_word) from [<c0424bf0>]
> (pci_check_pme_status+0x34/0x78)
> [<c0424bf0>] (pci_check_pme_status) from [<c0424c5c>] (pci_pme_wakeup+0x28/0x54)
> [<c0424c5c>] (pci_pme_wakeup) from [<c0424ce0>] (pci_pme_list_scan+0x58/0xb4)
> [<c0424ce0>] (pci_pme_list_scan) from [<c0235fbc>]
> (process_one_work+0x1bc/0x308)
> [<c0235fbc>] (process_one_work) from [<c02366c4>] (worker_thread+0x2a8/0x3e0)
> [<c02366c4>] (worker_thread) from [<c023a928>] (kthread+0xe4/0xfc)
> [<c023a928>] (kthread) from [<c0206d68>] (ret_from_fork+0x14/0x2c)
> Code: ea000000 e5903000 f57ff04f e3a00000 (e5843000)
> ---[ end trace 667d43ba3aa9e589 ]---
>
> Reported-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>
> Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> Cc: Mika Westerberg <mika.westerberg@linux.intel.com>
> Cc: Simon Horman <horms@verge.net.au>
> Cc: Yinghai Lu <yinghai@kernel.org>
> Fixes: df17e62e5bff ("PCI: Add support for polling PME state on suspended legacy PCI devices")
> Signed-off-by: Lukas Wunner <lukas@wunner.de>

Tested-by: Geert Uytterhoeven <geert+renesas@glider.be>

> ---
> drivers/pci/pci.c | 9 +++++----
> 1 file changed, 5 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index aa55501..c561a9e 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -1784,8 +1784,8 @@ static void pci_pme_list_scan(struct work_struct *work)
> }
> }
> if (!list_empty(&pci_pme_list))
> - schedule_delayed_work(&pci_pme_work,
> - msecs_to_jiffies(PME_TIMEOUT));
> + queue_delayed_work(system_freezable_wq, &pci_pme_work,
> + msecs_to_jiffies(PME_TIMEOUT));
> mutex_unlock(&pci_pme_list_mutex);
> }
>
> @@ -1850,8 +1850,9 @@ void pci_pme_active(struct pci_dev *dev, bool enable)
> mutex_lock(&pci_pme_list_mutex);
> list_add(&pme_dev->list, &pci_pme_list);
> if (list_is_singular(&pci_pme_list))
> - schedule_delayed_work(&pci_pme_work,
> - msecs_to_jiffies(PME_TIMEOUT));
> + queue_delayed_work(system_freezable_wq,
> + &pci_pme_work,
> + msecs_to_jiffies(PME_TIMEOUT));
> mutex_unlock(&pci_pme_list_mutex);
> } else {
> mutex_lock(&pci_pme_list_mutex);
> --
> 2.11.0

Gr{oetje,eeting}s,

Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
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