Date:   Tue, 20 Aug 2019 11:56:07 +0000
From:   Joakim Zhang <qiangqing.zhang@....com>
To:     Sean Nyekjaer <sean@...nix.com>,
        "mkl@...gutronix.de" <mkl@...gutronix.de>,
        "linux-can@...r.kernel.org" <linux-can@...r.kernel.org>
CC:     "wg@...ndegger.com" <wg@...ndegger.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        dl-linux-imx <linux-imx@....com>,
        Martin Hundebøll <martin@...nix.com>
Subject: RE: [PATCH REPOST 1/2] can: flexcan: fix deadlock when using self
 wakeup


> -----Original Message-----
> From: Joakim Zhang
> Sent: 2019年8月20日 19:25
> To: Sean Nyekjaer <sean@...nix.com>; mkl@...gutronix.de;
> linux-can@...r.kernel.org
> Cc: wg@...ndegger.com; netdev@...r.kernel.org; dl-linux-imx
> <linux-imx@....com>; Martin Hundebøll <martin@...nix.com>
> Subject: RE: [PATCH REPOST 1/2] can: flexcan: fix deadlock when using self
> wakeup
> 
> 
> > -----Original Message-----
> > From: Sean Nyekjaer <sean@...nix.com>
> > Sent: 2019年8月20日 18:25
> > To: Joakim Zhang <qiangqing.zhang@....com>; mkl@...gutronix.de;
> > linux-can@...r.kernel.org
> > Cc: wg@...ndegger.com; netdev@...r.kernel.org; dl-linux-imx
> > <linux-imx@....com>; Martin Hundebøll <martin@...nix.com>
> > Subject: Re: [PATCH REPOST 1/2] can: flexcan: fix deadlock when using
> > self wakeup
> >
> >
> >
> > On 16/08/2019 10.20, Joakim Zhang wrote:
> > > As reproted by Sean Nyekjaer below:
> > > When suspending, when there is still can traffic on the interfaces
> > > the flexcan immediately wakes the platform again. As it should :-).
> > > But it throws this error msg:
> > > [ 3169.378661] PM: noirq suspend of devices failed
> > >
> > > On the way down to suspend the interface that throws the error
> > > message does call flexcan_suspend but fails to call flexcan_noirq_suspend.
> > > That means the flexcan_enter_stop_mode is called, but on the way out
> > > of suspend the driver only calls flexcan_resume and skips
> > > flexcan_noirq_resume, thus it doesn't call flexcan_exit_stop_mode.
> > > This leaves the flexcan in stop mode, and with the current driver it
> > > can't recover from this even with a soft reboot, it requires a hard reboot.
> > >
> > > The best way to exit stop mode is in Wake Up interrupt context, and
> > > then
> > > suspend() and resume() functions can be symmetric. However, stop
> > > mode request and ack will be controlled by SCU(System Control Unit)
> > > firmware(manage clock,power,stop mode, etc. by Cortex-M4 core) in
> > > coming i.MX8(QM/QXP). And SCU firmware interface can't be available
> > > in
> > interrupt context.
> > >
> > > For compatibillity, the wake up mechanism can't be symmetric, so we
> > > need in_stop_mode hack.
> > >
> > > Fixes: de3578c198c6 ("can: flexcan: add self wakeup support")
> > > Reported-by: Sean Nyekjaer <sean@...nix.com>
> > > Signed-off-by: Joakim Zhang <qiangqing.zhang@....com>
> > >
> >
> > Unfortunatly it's still possible to reproduce the deadlock with this patch...
> >
> > [  689.921717] flexcan: probe of 2094000.flexcan failed with error
> > -110
> >
> > My test setup:
> > PC with CAN-USB dongle connected to can0 and can1.
> >
> > PC:
> > $ while true; do cansend can0 '123#DEADBEEF'; done
> >
> > iMX6ull:
> > root@...26:~# systemctl suspend
> >
> >
> > [  365.858054] systemd[1]: Reached target Sleep.
> > root@...26:~# [  365.939826] systemd[1]: Starting Suspend...
> > [  366.115839] systemd-sleep[248]: Suspending system...
> > [  366.517949] dpm_run_callback(): platform_pm_suspend+0x0/0x5c
> > returns
> > -110 [  366.518249] PM: Device 2094000.flexcan failed to suspend:
> > error -110 [  366.518406] PM: Some devices failed to suspend, or early
> > wake event detected [  366.732162] dpm_run_callback():
> > platform_pm_suspend+0x0/0x5c returns -110 [  366.732285] PM: Device
> > 2090000.flexcan failed to suspend: error -110 [  366.732330] PM: Some
> > devices failed to suspend, or early wake event detected [  366.890637]
> > systemd-sleep[248]: System resumed.
> 
> CAN1, CAN0 suspended failed, then CAN0, CAN1 resumed back, so
> CAN0/CAN1 can work fine.
>
> > [  366.923062] systemd[1]: Started Suspend.
> > [  366.942819] systemd[1]: sleep.target: Unit not needed anymore.
> Stopping.
> > [  366.954791] systemd[1]: Stopped target Sleep.
> > [  366.962402] systemd[1]: Reached target Suspend.
> > [  366.977546] systemd-logind[135]: Operation 'sleep' finished.
> > [  366.979194] systemd[1]: suspend.target: Unit not needed anymore.
> > Stopping.
> > [  366.993831] systemd[1]: Stopped target Suspend.
> > [  367.139972] systemd-networkd[220]: usb0: Lost carrier [
> > 367.294077]
> > systemd-networkd[220]: usb0: Gained carrier
> >
> > root@...26:~# candump can0 | head -n 2
> >
> >    can0  123   [4]  DE AD BE EF
> >    can0  123   [4]  DE AD BE EF
> > root@...26:~# candump can1 | head -n 2
> >
> >    can1  123   [4]  DE AD BE EF
> >    can1  123   [4]  DE AD BE EF
> > root@...26:~# systemctl suspend
> >
> > root@...26:~# [  385.106658] systemd[1]: Reached target Sleep.
> > [  385.147602] systemd[1]: Starting Suspend...
> > [  385.246421] systemd-sleep[260]: Suspending system...
> > [  385.634733] dpm_run_callback(): platform_pm_suspend+0x0/0x5c
> > returns
> > -110 [  385.634855] PM: Device 2090000.flexcan failed to suspend:
> > error -110 [  385.634897] PM: Some devices failed to suspend, or early
> > wake event detected [  385.856251] PM: noirq suspend of devices failed
> > [  385.998364]
> > systemd-sleep[260]: System resumed.
> 
> CAN0 suspended failed, CAN1 noirq suspended failed, then CAN1, CAN0
> resumed back, so CAN0/CAN1 can work fine.

If CAN0 suspended failed, should system resumed after suspended all devices, should not enter noirq suspend, 
why it here printed "PM: noirq suspend of devices failed"?

> > [  386.023390] systemd[1]: Started Suspend.
> > [  386.031570] systemd[1]: sleep.target: Unit not needed anymore.
> Stopping.
> > [  386.055886] systemd[1]: Stopped target Sleep.
> > [  386.061430] systemd[1]: Reached target Suspend.
> > [  386.066142] systemd[1]: suspend.target: Unit not needed anymore.
> > Stopping.
> > [  386.112575] systemd-networkd[220]: usb0: Lost carrier [
> > 386.116797]
> > systemd-logind[135]: Operation 'sleep' finished.
> > [  386.146161] systemd[1]: Stopped target Suspend.
> > [  386.260866] systemd-networkd[220]: usb0: Gained carrier
> > root@...26:~# candump can0 | head -n 2
> >    can0  123   [4]  DE AD BE EF
> >    can0  123   [4]  DE AD BE EF
> > root@...26:~# candump can1 | head -n 2
> >
> >    can1  123   [4]  DE AD BE EF
> >    can1  123   [4]  DE AD BE EF
> > root@...26:~# systemctl suspend
> >
> > [  396.919303] systemd[1]: Reached target Sleep.
> > root@...26:~# [  396.964722] systemd[1]: Starting Suspend...
> > [  397.067336] systemd-sleep[268]: Suspending system...
> > [  397.574571] PM: noirq suspend of devices failed [  397.834731] PM:
> > noirq suspend of devices failed [  397.807996] systemd-networkd[220]:
> > usb0: Lost carrier [  398.156295] dpm_run_callback():
> > platform_pm_suspend+0x0/0x5c returns -110 [  398.156339] PM: Device
> 2094000.flexcan failed to suspend:
> > error -110 [  398.156509] PM: Some devices failed to suspend, or early
> > wake event detected [  398.053555] systemd-sleep[268]: Failed to write
> > /sys/power/state:
> > Device or resource busy
> 
> But the log here is very strange and chaotic, it looks like CAN0 suspended failed,
> then resumed back, so CAN0 can work fine.
> CAN1 noirq suspend failed, but have not resumed back, so CAN1 still in stop
> mode, cannot work. I think this may be other device noirq suspend failed broke
> the resume of CAN1.
> 
> Could you do more debug to help locate the issue?

More strange, why here first enter noirq suspend?

Best Regards,
Joakim Zhang
> > [  398.074751] systemd[1]: systemd-suspend.service: Main process
> > exited, code=exited, status=1/FAILURE [  398.076779] systemd[1]:
> 
> > systemd-suspend.service: Failed with result 'exit-code'.
> > [  398.109255] systemd[1]: Failed to start Suspend.
> > [  398.118704] systemd[1]: Dependency failed for Suspend.
> > [  398.136283] systemd-logind[135]: Operation 'sleep' finished.
> > [  398.137770] systemd[1]: suspend.target: Job suspend.target/start
> > failed with result 'dependency'.
> > [  398.139105] systemd[1]: sleep.target: Unit not needed anymore.
> Stopping.
> > [  398.167590] systemd[1]: Stopped target Sleep.
> > [  398.201558] systemd-networkd[220]: usb0: Gained carrier
> 
> Log here also strange.
> 
> Best Regards,
> Joakim Zhang
> > root@...26:~# candump can0 | head -n 2
> >    can0  123   [4]  DE AD BE EF
> >    can0  123   [4]  DE AD BE EF
> > root@...26:~# candump can1 | head -n 2
> >
> > nothing on can1 anymore :-(
> >
> > root@...26:~# rmmod flexcan
> > [  622.884746] systemd-networkd[220]: can1: Lost carrier [
> > 623.046766]
> > systemd-networkd[220]: can0: Lost carrier root@...26:~# insmod
> > /mnt/flexcan.ko [  628.323981] flexcan 2094000.flexcan: registering
> > netdev failed
> >
> > and can1 fails to register with:
> > [  628.347485] flexcan: probe of 2094000.flexcan failed with error
> > -110
> >
> > /Sean

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