WARNING: suspicious RCU usage

[Paul E. McKenney]

On Tue, Dec 12, 2017 at 04:11:07PM -0200, Fabio Estevam wrote:
> Hi Russell,
> 
> On Tue, Dec 12, 2017 at 3:34 PM, Russell King - ARM Linux
> <linux at armlinux.org.uk> wrote:
> 
> > It's fundamentally unsafe.
> >
> > You need to test with CONFIG_BL_SWITCHER enabled - there's spinlocks
> > in smp_call_function_single() path that are conditional on that symbol.
> > If CONFIG_BL_SWITCHER is disabled, then the spinlocks are not present.
> 
> Ok, just tested with CONFIG_BL_SWITCHER=y on a imx6q-cubox-i:

Just to confirm, your dmesg below is illustrating the hang, correct?

							Thanx, Paul

> # echo enabled > /sys/class/tty/ttymxc0/power/wakeup
> # echo mem > /sys/power/state
> [   10.503462] PM: suspend entry (deep)
> [   10.507479] PM: Syncing filesystems ... done.
> [   10.555024] Freezing user space processes ... (elapsed 0.002 seconds) done.
> [   10.564511] OOM killer disabled.
> [   10.567760] Freezing remaining freezable tasks ... (elapsed 0.002 seconds) d.
> [   10.577420] Suspending console(s) (use no_console_suspend to debug)
> [   10.657748] PM: suspend devices took 0.080 seconds
> [   10.669329] Disabling non-boot CPUs ...
> [   10.717049] IRQ17 no longer affine to CPU1
> [   10.837141] Enabling non-boot CPUs ...
> [   10.839386] CPU1 is up
> [   10.840342] CPU2 is up
> [   10.841300] CPU3 is up
> [   11.113735] mmc0: queuing unknown CIS tuple 0x80 (2 bytes)
> [   11.115676] mmc0: queuing unknown CIS tuple 0x80 (3 bytes)
> [   11.117595] mmc0: queuing unknown CIS tuple 0x80 (3 bytes)
> [   11.121014] mmc0: queuing unknown CIS tuple 0x80 (7 bytes)
> [   11.124454] mmc0: queuing unknown CIS tuple 0x80 (7 bytes)
> [   11.177299] ata1: SATA link down (SStatus 0 SControl 300)
> [   11.181930] PM: resume devices took 0.330 seconds
> [   11.243729] OOM killer enabled.
> [   11.246886] Restarting tasks ... done.
> [   11.253012] PM: suspend exit
>