mx6: suspicious RCU usage

[Paul E. McKenney]

On Tue, Jul 14, 2015 at 09:00:06AM -0700, Paul E. McKenney wrote:
> On Tue, Jul 14, 2015 at 12:54:15PM -0300, Fabio Estevam wrote:
> > Hi,
> > 
> > I am running 4.2-rc2 on a mx6q board and I see the following warning
> > when doing a suspend/resume cycle:
> > 
> > $ echo mem > /sys/power/state
> > 
> > PM: Syncing filesystems ... done.
> > Freezing user space processes ... (elapsed 0.003 seconds) done.
> > Freezing remaining freezable tasks ... (elapsed 0.003 seconds) done.
> > Suspending console(s) (use no_console_suspend to debug)
> > 
> > (Press GPIO button to wake up the system)
> > 
> > PM: suspend of devices complete after 101.667 msecs
> > PM: suspend devices took 0.110 seconds
> > PM: late suspend of devices complete after 11.073 msecs
> > PM: noirq suspend of devices complete after 9.432 msecs
> > Disabling non-boot CPUs ...
> 
> Does this patch help?
> 
> 	https://lkml.org/lkml/2015/5/12/885

Or this one, if this is ARM rather than ARM64:

	https://lkml.org/lkml/2015/5/12/892

							Thanx, Paul

> > ===============================
> > [ INFO: suspicious RCU usage. ]
> > 4.2.0-rc2 #247 Not tainted
> > -------------------------------
> > kernel/sched/fair.c:5032 suspicious rcu_dereference_check() usage!
> > 
> > other info that might help us debug this:
> > 
> > 
> > RCU used illegally from offline CPU!
> > rcu_scheduler_active = 1, debug_locks = 0
> > 3 locks held by swapper/1/0:
> >  #0:  ((cpu_died).wait.lock){......}, at: [<800643e0>] complete+0x1c/0x4c
> >  #1:  (&p->pi_lock){-.-.-.}, at: [<8004f7e8>] try_to_wake_up+0x34/0x3c8
> >  #2:  (rcu_read_lock){......}, at: [<80057b68>] select_task_rq_fair+0x64/0x9e8
> > 
> > stack backtrace:
> > CPU: 1 PID: 0 Comm: swapper/1 Not tainted 4.2.0-rc2 #247
> > Hardware name: Freescale i.MX6 Quad/DualLite (Device Tree)
> > Backtrace:
> > [<80012ee8>] (dump_backtrace) from [<80013084>] (show_stack+0x18/0x1c)
> >  r6:000013a8 r5:00000000 r4:00000000 r3:00000000
> > [<8001306c>] (show_stack) from [<8078d364>] (dump_stack+0x88/0xa4)
> > [<8078d2dc>] (dump_stack) from [<800676d8>] (lockdep_rcu_suspicious+0xbc/0x11c)
> >  r5:809497c4 r4:be076780
> > [<8006761c>] (lockdep_rcu_suspicious) from [<80058200>]
> > (select_task_rq_fair+0x6fc/0x9e8)
> >  r7:80a94fc0 r6:00000001 r5:00000000 r4:00000000
> > [<80057b04>] (select_task_rq_fair) from [<8004f8cc>]
> > (try_to_wake_up+0x118/0x3c8)
> >  r10:80a94fc0 r9:00000000 r8:00000000 r7:80000093 r6:80a98b2c r5:bd748f8c
> >  r4:bd748b80
> > [<8004f7b4>] (try_to_wake_up) from [<8004fb90>]
> > (default_wake_function+0x14/0x18)
> >  r10:00000003 r9:8004fb7c r8:00000000 r7:00000000 r6:80a9dc34 r5:00000001
> >  r4:80a9dc28
> > [<8004fb7c>] (default_wake_function) from [<80063b18>]
> > (__wake_up_common+0x58/0x98)
> > [<80063ac0>] (__wake_up_common) from [<80063b74>] (__wake_up_locked+0x1c/0x24)
> >  r10:80a98b2c r9:807993ac r8:80a98a10 r7:80afc552 r6:60000093 r5:80a9dc10
> >  r4:80a9dc14
> > [<80063b58>] (__wake_up_locked) from [<80064400>] (complete+0x3c/0x4c)
> > [<800643c4>] (complete) from [<807870e0>] (cpu_die+0x3c/0xa4)
> >  r6:80a923e4 r5:00000001 r4:80a98968 r3:00000002
> > [<807870a4>] (cpu_die) from [<80010798>] (arch_cpu_idle_dead+0x10/0x14)
> >  r5:80a989c4 r4:00000000
> > [<80010788>] (arch_cpu_idle_dead) from [<80064798>]
> > (cpu_startup_entry+0x1d8/0x200)
> > [<800645c0>] (cpu_startup_entry) from [<80015e34>]
> > (secondary_start_kernel+0x120/0x13c)
> >  r7:80aff360
> > [<80015d14>] (secondary_start_kernel) from [<1000962c>] (0x1000962c)
> >  r5:00000015 r4:4e08806a
> > CPU1: shutdown
> > CPU2: shutdown
> > CPU3: shutdown
> > Enabling non-boot CPUs ...
> > CPU1 is up
> > CPU2 is up
> > CPU3 is up
> > PM: noirq resume of devices complete after 2.185 msecs
> > PM: early resume of devices complete after 2.786 msecs
> > PM: resume of devices complete after 204.223 msecs
> > PM: resume devices took 0.200 seconds
> > ata1: SATA link down (SStatus 0 SControl 300)
> > PM: Finishing wakeup.
> > Restarting tasks ... done.
> > 
> > I haven't started bisecting it yet, but if someone has some ideas,
> > please let me know.
> > 
> > Regards,
> > 
> > Fabio Estevam
> >