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Date: Tue, 1 Apr 2014 10:55:45 -0700 From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> To: Dave Jones <davej@...hat.com>, Linux Kernel <linux-kernel@...r.kernel.org> Subject: Re: rcu_prempt stalls / lockup On Tue, Apr 01, 2014 at 01:22:44PM -0400, Dave Jones wrote: > On Tue, Apr 01, 2014 at 08:30:32AM -0700, Paul E. McKenney wrote: > > > [14403.765300] INFO: rcu_preempt detected stalls on CPUs/tasks: > > > [14403.766405] (detected by 0, t=260067 jiffies, g=449892, c=449891, q=0) > > > and on and on.. > > > > > > so kernel space still works like before, but userspace is locked up. > > > > Interesting. I suspect that if you reverted the rest of this merge > > window's RCU patches, you would get the same result. > > > > > > If that doesn't work, I will need to put together some diagnostic patches. > > > > Starting with the one below. > > > > > > bugger, I forgot to apply this last night. I'll do it on the next run. > > > > But let's see what this shows first. > > [ 1173.923463] INFO: rcu_preempt detected stalls on CPUs/tasks: > [ 1173.924457] (detected by 0, t=6502 jiffies, g=47728, c=47727, q=0) > [ 1173.925199] INFO: Stall ended before state dump start, gp_kthread state: 0x2 > [ 1368.859744] INFO: rcu_preempt detected stalls on CPUs/tasks: > [ 1368.860754] (detected by 0, t=26007 jiffies, g=47728, c=47727, q=0) > [ 1368.861559] INFO: Stall ended before state dump start, gp_kthread state: 0x2 > [ 1563.796416] INFO: rcu_preempt detected stalls on CPUs/tasks: > [ 1563.797426] (detected by 0, t=45512 jiffies, g=47728, c=47727, q=0) > [ 1563.798293] INFO: Stall ended before state dump start, gp_kthread state: 0x2 > [ 1758.733747] INFO: rcu_preempt detected stalls on CPUs/tasks: > [ 1758.734725] (detected by 0, t=65017 jiffies, g=47728, c=47727, q=0) > [ 1758.735526] INFO: Stall ended before state dump start, gp_kthread state: 0x2 > [ 1953.670944] INFO: rcu_preempt detected stalls on CPUs/tasks: > [ 1953.671932] (detected by 0, t=84522 jiffies, g=47728, c=47727, q=0) > [ 1953.672735] INFO: Stall ended before state dump start, gp_kthread state: 0x2 > [ 2148.608132] INFO: rcu_preempt detected stalls on CPUs/tasks: > [ 2148.609140] (detected by 0, t=104027 jiffies, g=47728, c=47727, q=0) > etc etc. Waiting uninterruptibly. Presumably blocked on mutex_lock(). But you have CONFIG_PROVE_LOCKING(), so any deadlocks should have been reported. Given that you have CONFIG_RCU_TRACE=y, could you please enable the following trace events and dump the trace before things hang? trace_event=rcu:rcu_grace_period,rcu:rcu_grace_period_init If it is not feasible to dump the trace before things hang, let me know, and I will work out some other diagnostic regime. Thanx, Paul -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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