Re: rcu_prempt stalls / lockup

From: Paul E. McKenney
Date: Tue Apr 01 2014 - 20:00:42 EST

On Tue, Apr 01, 2014 at 07:31:30PM -0400, Dave Jones wrote:
> On Tue, Apr 01, 2014 at 04:18:22PM -0700, Paul E. McKenney wrote:
>
> > > # entries-in-buffer/entries-written: 7/7 #P:4
> > > #
> > > # _-----=> irqs-off
> > > # / _----=> need-resched
> > > # | / _---=> hardirq/softirq
> > > # || / _--=> preempt-depth
> > > # ||| / delay
> > > # TASK-PID CPU# |||| TIMESTAMP FUNCTION
> > > # | | | |||| | |
> > > <idle>-0 [000] dNs3 851.748475: rcu_grace_period: rcu_preempt 21342 cpuend
> > > <idle>-0 [000] dNs3 851.748477: rcu_grace_period: rcu_preempt 21343 cpustart
> > > <idle>-0 [000] dNs3 851.748477: rcu_grace_period: rcu_sched 20080 cpuend
> > > <idle>-0 [000] dN.2 851.748480: rcu_grace_period: rcu_preempt 21343 cpuqs
> > > rcu_preempt-9 [000] ...1 851.748485: rcu_grace_period: rcu_preempt 21343 fqsstart
> > > rcu_preempt-9 [000] ...1 851.748487: rcu_grace_period: rcu_preempt 21343 fqsend
> > > rcu_preempt-9 [000] ...1 851.748487: rcu_grace_period: rcu_preempt 21343 fqswait
> > > # tracer: nop
> > > #
> > > # entries-in-buffer/entries-written: 13/13 #P:4
> > > #
> > > # _-----=> irqs-off
> > > # / _----=> need-resched
> > > # | / _---=> hardirq/softirq
> > > # || / _--=> preempt-depth
> > > # ||| / delay
> > > # TASK-PID CPU# |||| TIMESTAMP FUNCTION
> > > # | | | |||| | |
> > > rcu_preempt-9 [003] d..2 851.878457: rcu_grace_period: rcu_preempt 21349 end
> > > rcu_preempt-9 [003] d..2 851.878459: rcu_grace_period: rcu_preempt 21349 newreq
> > > rcu_preempt-9 [003] ...1 851.878459: rcu_grace_period: rcu_preempt 21349 reqwait
> > > rcu_preempt-9 [003] d..2 851.878460: rcu_grace_period: rcu_preempt 21350 start
> > > rcu_preempt-9 [003] d..2 851.878461: rcu_grace_period: rcu_preempt 21350 cpustart
> > > rcu_preempt-9 [003] d..2 851.878462: rcu_grace_period_init: rcu_preempt 21350 0 0 7 f
> > > rcu_preempt-9 [003] ...1 851.878463: rcu_grace_period: rcu_preempt 21350 fqswait
> > > rcu_preempt-9 [003] d..2 851.878464: rcu_grace_period: rcu_preempt 21350 cpuqs
> > > <idle>-0 [000] dNs3 851.878482: rcu_grace_period: rcu_preempt 21349 cpuend
> > > <idle>-0 [000] dNs3 851.878483: rcu_grace_period: rcu_preempt 21350 cpustart
> > > <idle>-0 [000] dNs3 851.878484: rcu_grace_period: rcu_sched 20086 cpuend
> > > <idle>-0 [000] .N.2 851.878486: rcu_grace_period: rcu_sched 20086 cpuqs
> > > <idle>-0 [000] dN.2 851.878487: rcu_grace_period: rcu_preempt 21350 cpuqs

OK, so the trace ended on grace period #21350...

> > >
> > >
> > > followed by a half dozen 'empty' traces before it totally locked up.
> >
> > Cool, thank you!
> >
> > Could you please also send the RCU CPU stall warning messages?
>
> >From that run they were..
>
> [ 917.790265] INFO: rcu_preempt detected stalls on CPUs/tasks:
> [ 917.791189] (detected by 0, t=6502 jiffies, g=21390, c=21389, q=0)

But the hang didn't happen until grace period #21390. Sigh! That means
that the trace doesn't tell me about the current grace period.

Thank you for getting this info, but it is beginning to look like
bisection is necessary here. :-(

Thanx, Paul

> [ 917.792058] INFO: Stall ended before state dump start, gp_kthread state: 0x2
> [ 917.792799] INFO: rcu_sched detected stalls on CPUs/tasks:
> [ 917.793534] (detected by 0, t=6502 jiffies, g=20128, c=20127, q=0)
> [ 917.794265] INFO: Stall ended before state dump start, gp_kthread state: 0x2
> [ 1112.727480] INFO: rcu_preempt detected stalls on CPUs/tasks:
> [ 1112.728425] (detected by 0, t=26007 jiffies, g=21390, c=21389, q=0)
> [ 1112.729300] INFO: Stall ended before state dump start, gp_kthread state: 0x2
> [ 1112.730035] INFO: rcu_sched detected stalls on CPUs/tasks:
> [ 1112.730744] (detected by 0, t=26007 jiffies, g=20128, c=20127, q=0)
> [ 1112.731459] INFO: Stall ended before state dump start, gp_kthread state: 0x2
> [ 1307.664710] INFO: rcu_preempt detected stalls on CPUs/tasks:
> [ 1307.665623] (detected by 0, t=45512 jiffies, g=21390, c=21389, q=0)
> [ 1307.666386] INFO: Stall ended before state dump start, gp_kthread state: 0x2
> [ 1307.667113] INFO: rcu_sched detected stalls on CPUs/tasks:
> [ 1307.667839] (detected by 0, t=45512 jiffies, g=20128, c=20127, q=0)
> [ 1307.668572] INFO: Stall ended before state dump start, gp_kthread state: 0x2
> [ 1502.601961] INFO: rcu_preempt detected stalls on CPUs/tasks:
> [ 1502.602905] (detected by 0, t=65017 jiffies, g=21390, c=21389, q=0)
> [ 1502.603765] INFO: Stall ended before state dump start, gp_kthread state: 0x2
> [ 1502.604550] INFO: rcu_sched detected stalls on CPUs/tasks:
> [ 1502.605305] (detected by 0, t=65017 jiffies, g=20128, c=20127, q=0)
> [ 1502.606061] INFO: Stall ended before state dump start, gp_kthread state: 0x2
> [ 1697.539217] INFO: rcu_preempt detected stalls on CPUs/tasks:
> [ 1697.540189] (detected by 0, t=84522 jiffies, g=21390, c=21389, q=0)
> [ 1697.541052] INFO: Stall ended before state dump start, gp_kthread state: 0x2
> [ 1697.541826] INFO: rcu_sched detected stalls on CPUs/tasks:
> [ 1697.542600] (detected by 0, t=84522 jiffies, g=20128, c=20127, q=0)
> [ 1697.543378] INFO: Stall ended before state dump start, gp_kthread state: 0x2
> [ 1892.476433] INFO: rcu_preempt detected stalls on CPUs/tasks:
> [ 1892.477545] (detected by 0, t=104027 jiffies, g=21390, c=21389, q=0)
> [ 1892.478402] INFO: Stall ended before state dump start, gp_kthread state: 0x2
> [ 1892.479208] INFO: rcu_sched detected stalls on CPUs/tasks:
> [ 1892.480010] (detected by 0, t=104027 jiffies, g=20128, c=20127, q=0)
> [ 1892.480831] INFO: Stall ended before state dump start, gp_kthread state: 0x2
> [ 2087.413694] INFO: rcu_preempt detected stalls on CPUs/tasks:
> [ 2087.414748] (detected by 0, t=123532 jiffies, g=21390, c=21389, q=0)
> [ 2087.415722] INFO: Stall ended before state dump start, gp_kthread state: 0x2
> [ 2087.416558] INFO: rcu_sched detected stalls on CPUs/tasks:
> [ 2087.417392] (detected by 0, t=123532 jiffies, g=20128, c=20127, q=0)
> [ 2087.418231] INFO: Stall ended before state dump start, gp_kthread state: 0x2
>
>
>

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