Hi Paul, I've been running with your patch below for a while now, and haven't encountered the issue again. On 07/01/2012 03:15 AM, Paul E. McKenney wrote: > On Fri, Jun 29, 2012 at 06:44:41PM +0200, Sasha Levin wrote: >> Hi all, >> >> While fuzzing using trinity on a KVM tools guest with todays linux-next, I've hit the following lockup: >> >> [ 362.261729] INFO: task numad/2:27 blocked for more than 120 seconds. >> [ 362.263974] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. >> [ 362.271684] numad/2 D 0000000000000001 5672 27 2 0x00000000 >> [ 362.280052] ffff8800294c7c58 0000000000000046 ffff8800294c7c08 ffffffff81163dba >> [ 362.294477] ffff8800294c6000 ffff8800294c6010 ffff8800294c7fd8 ffff8800294c6000 >> [ 362.306631] ffff8800294c6010 ffff8800294c7fd8 ffff88000d5c3000 ffff8800294c8000 >> [ 362.315395] Call Trace: >> [ 362.318556] [<ffffffff81163dba>] ? __lock_release+0x1ba/0x1d0 >> [ 362.325411] [<ffffffff8372ab75>] schedule+0x55/0x60 >> [ 362.328844] [<ffffffff8372b965>] rwsem_down_failed_common+0xf5/0x130 >> [ 362.332501] [<ffffffff8115d38e>] ? put_lock_stats+0xe/0x40 >> [ 362.334496] [<ffffffff81160135>] ? __lock_contended+0x1f5/0x230 >> [ 362.336723] [<ffffffff8372b9d5>] rwsem_down_read_failed+0x15/0x17 >> [ 362.339297] [<ffffffff81985e34>] call_rwsem_down_read_failed+0x14/0x30 >> [ 362.341768] [<ffffffff83729a29>] ? down_read+0x79/0xa0 >> [ 362.343669] [<ffffffff8122d262>] ? lazy_migrate_process+0x22/0x60 >> [ 362.345616] [<ffffffff8122d262>] lazy_migrate_process+0x22/0x60 >> [ 362.347464] [<ffffffff811453c0>] process_mem_migrate+0x10/0x20 >> [ 362.349340] [<ffffffff81145090>] move_processes+0x190/0x230 >> [ 362.351398] [<ffffffff81145b7a>] numad_thread+0x7a/0x120 >> [ 362.353245] [<ffffffff81145b00>] ? find_busiest_node+0x310/0x310 >> [ 362.355396] [<ffffffff81119e82>] kthread+0xb2/0xc0 >> [ 362.356996] [<ffffffff8372ea34>] kernel_thread_helper+0x4/0x10 >> [ 362.359253] [<ffffffff8372ccb4>] ? retint_restore_args+0x13/0x13 >> [ 362.361168] [<ffffffff81119dd0>] ? __init_kthread_worker+0x70/0x70 >> [ 362.363277] [<ffffffff8372ea30>] ? gs_change+0x13/0x13 >> >> I've hit sysrq-t to see what might be the cause, and it appears that an OOM was in progress, and was stuck on RCU: >> >> [ 578.086230] trinity-child69 D ffff8800277a54c8 3968 6658 6580 0x00000000 >> [ 578.086230] ffff880022c5f518 0000000000000046 ffff880022c5f4c8 ffff88001b9d6e00 >> [ 578.086230] ffff880022c5e000 ffff880022c5e010 ffff880022c5ffd8 ffff880022c5e000 >> [ 578.086230] ffff880022c5e010 ffff880022c5ffd8 ffff880023c08000 ffff880022c33000 >> [ 578.086230] Call Trace: >> [ 578.086230] [<ffffffff8372ab75>] schedule+0x55/0x60 >> [ 578.086230] [<ffffffff837285c8>] schedule_timeout+0x38/0x2c0 >> [ 578.086230] [<ffffffff81161d16>] ? mark_held_locks+0xf6/0x120 >> [ 578.086230] [<ffffffff81163dba>] ? __lock_release+0x1ba/0x1d0 >> [ 578.086230] [<ffffffff8372c67b>] ? _raw_spin_unlock_irq+0x2b/0x80 >> [ 578.086230] [<ffffffff8372a06f>] wait_for_common+0xff/0x170 >> [ 578.086230] [<ffffffff81132c10>] ? try_to_wake_up+0x290/0x290 >> [ 578.086230] [<ffffffff8372a188>] wait_for_completion+0x18/0x20 >> [ 578.086230] [<ffffffff811a5de7>] _rcu_barrier+0x4a7/0x4e0 > > Hmmm... Perhaps a blocking operation is not appropriate here. I have > substituted a nonblocking approach, which is at -rcu (thus soon -next) > at 1ee4c09d (Provide OOM handler to motivate lazy RCU callbacks). > Patch below. > > Thanx, Paul > > ------------------------------------------------------------------------ > > rcu: Provide OOM handler to motivate lazy RCU callbacks > > In kernels built with CONFIG_RCU_FAST_NO_HZ=y, CPUs can accumulate a > large number of lazy callbacks, which as the name implies will be slow > to be invoked. This can be a problem on small-memory systems, where the > default 6-second sleep for CPUs having only lazy RCU callbacks could well > be fatal. This commit therefore installs an OOM hander that ensures that > every CPU with non-lazy callbacks has at least one non-lazy callback, > in turn ensuring timely advancement for these callbacks. > > Signed-off-by: Paul E. McKenney <paul.mckenney@xxxxxxxxxx> > Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> > > diff --git a/kernel/rcutree.h b/kernel/rcutree.h > index 4b47fbe..dab279f 100644 > --- a/kernel/rcutree.h > +++ b/kernel/rcutree.h > @@ -314,8 +314,11 @@ struct rcu_data { > unsigned long n_rp_need_fqs; > unsigned long n_rp_need_nothing; > > - /* 6) _rcu_barrier() callback. */ > + /* 6) _rcu_barrier() and OOM callbacks. */ > struct rcu_head barrier_head; > +#ifdef CONFIG_RCU_FAST_NO_HZ > + struct rcu_head oom_head; > +#endif /* #ifdef CONFIG_RCU_FAST_NO_HZ */ > > int cpu; > struct rcu_state *rsp; > diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h > index 81e53eb..1908847 100644 > --- a/kernel/rcutree_plugin.h > +++ b/kernel/rcutree_plugin.h > @@ -25,6 +25,7 @@ > */ > > #include <linux/delay.h> > +#include <linux/oom.h> > > #define RCU_KTHREAD_PRIO 1 > > @@ -2128,6 +2129,90 @@ static void rcu_idle_count_callbacks_posted(void) > __this_cpu_add(rcu_dynticks.nonlazy_posted, 1); > } > > +/* > + * Data for flushing lazy RCU callbacks at OOM time. > + */ > +static atomic_t oom_callback_count; > +static DECLARE_WAIT_QUEUE_HEAD(oom_callback_wq); > + > +/* > + * RCU OOM callback -- decrement the outstanding count and deliver the > + * wake-up if we are the last one. > + */ > +static void rcu_oom_callback(struct rcu_head *rhp) > +{ > + if (atomic_dec_and_test(&oom_callback_count)) > + wake_up(&oom_callback_wq); > +} > + > +/* > + * Post an rcu_oom_notify callback on the current CPU if it has at > + * least one lazy callback. This will unnecessarily post callbacks > + * to CPUs that already have a non-lazy callback at the end of their > + * callback list, but this is an infrequent operation, so accept some > + * extra overhead to keep things simple. > + */ > +static void rcu_oom_notify_cpu(void *flavor) > +{ > + struct rcu_state *rsp = flavor; > + struct rcu_data *rdp = __this_cpu_ptr(rsp->rda); > + > + if (rdp->qlen_lazy != 0) { > + atomic_inc(&oom_callback_count); > + rsp->call(&rdp->oom_head, rcu_oom_callback); > + } > +} > + > +/* > + * If low on memory, ensure that each CPU has a non-lazy callback. > + * This will wake up CPUs that have only lazy callbacks, in turn > + * ensuring that they free up the corresponding memory in a timely manner. > + */ > +static int rcu_oom_notify(struct notifier_block *self, > + unsigned long notused, void *nfreed) > +{ > + int cpu; > + > + /* Wait for callbacks from earlier instance to complete. */ > + wait_event(oom_callback_wq, atomic_read(&oom_callback_count) == 0); > + > + /* > + * Prevent premature wakeup: ensure that all increments happen > + * before there is a chance of the counter reaching zero. > + */ > + atomic_set(&oom_callback_count, 1); > + > + get_online_cpus(); > + for_each_online_cpu(cpu) { > +#ifdef CONFIG_PREEMPT_RCU > + smp_call_function_single(cpu, rcu_oom_notify_cpu, > + &rcu_preempt_state, 1); > +#endif /* #ifdef CONFIG_PREEMPT_RCU */ > + smp_call_function_single(cpu, rcu_oom_notify_cpu, > + &rcu_bh_state, 1); > + smp_call_function_single(cpu, rcu_oom_notify_cpu, > + &rcu_sched_state, 1); > + } > + put_online_cpus(); > + > + /* Unconditionally decrement: no need to wake ourselves up. */ > + atomic_dec(&oom_callback_count); > + > + *(unsigned long *)nfreed = 1; > + return NOTIFY_OK; > +} > + > +static struct notifier_block rcu_oom_nb = { > + .notifier_call = rcu_oom_notify > +}; > + > +static int __init rcu_register_oom_notifier(void) > +{ > + register_oom_notifier(&rcu_oom_nb); > + return 0; > +} > +early_initcall(rcu_register_oom_notifier); > + > #endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */ > > #ifdef CONFIG_RCU_CPU_STALL_INFO > > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. 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