On Tue, Apr 26, 2011 at 8:50 PM, Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> wrote: > On Tue, Apr 26, 2011 at 10:12:39AM -0700, Linus Torvalds wrote: >> On Tue, Apr 26, 2011 at 9:38 AM, Bruno PrÃmont >> <bonbons@xxxxxxxxxxxxxxxxx> wrote: >> > >> > Here it comes: >> > >> > rcu_kthread (when build processes are STOPped): >> > [ Â836.050003] rcu_kthread   R running  7324   6   Â2 0x00000000 >> > [ Â836.050003] Âdd473f28 00000046 5a000240 dd65207c dd407360 dd651d40 0000035c dd473ed8 >> > [ Â836.050003] Âc10bf8a2 c14d63d8 dd65207c dd473f28 dd445040 dd445040 dd473eec c10be848 >> > [ Â836.050003] Âdd651d40 dd407360 ddfdca00 dd473f14 c10bfde2 00000000 00000001 000007b6 >> > [ Â836.050003] Call Trace: >> > [ Â836.050003] Â[<c10bf8a2>] ? check_object+0x92/0x210 >> > [ Â836.050003] Â[<c10be848>] ? init_object+0x38/0x70 >> > [ Â836.050003] Â[<c10bfde2>] ? free_debug_processing+0x112/0x1f0 >> > [ Â836.050003] Â[<c103d9fd>] ? lock_timer_base+0x2d/0x70 >> > [ Â836.050003] Â[<c13c8ec7>] schedule_timeout+0x137/0x280 >> >> Hmm. >> >> I'm adding Ingo and Peter to the cc, because this whole "rcu_kthread >> is running, but never actually running" is starting to smell like a >> scheduler issue. >> >> Peter/Ingo: RCUTINY seems to be broken for Bruno. During any kind of >> heavy workload, at some point it looks like rcu_kthread simply stops >> making any progress. It's constantly in runnable state, but it doesn't >> actually use any CPU time, and it's not processing the RCU callbacks, >> so the RCU memory freeing isn't happening, and slabs just build up >> until the machine dies. >> >> And it really is RCUTINY, because the thing doesn't happen with the >> regular tree-RCU. > > The difference between TINY_RCU and TREE_RCU is that TREE_RCU still uses > softirq for the core RCU processing. ÂTINY_RCU switched to a kthread > when I implemented RCU priority boosting. ÂThere is a similar change in > my -rcu tree that makes TREE_RCU use kthreads, and Sedat has been running > into a very similar problem with that change in place. ÂWhich is why I > do not yet push it to the -next tree. > >> This is without CONFIG_RCU_BOOST_PRIO, so we basically have >> >>     struct sched_param sp; >> >>     rcu_kthread_task = kthread_run(rcu_kthread, NULL, "rcu_kthread"); >>     sp.sched_priority = RCU_BOOST_PRIO; >>     sched_setscheduler_nocheck(rcu_kthread_task, SCHED_FIFO, &sp); >> >> where RCU_BOOST_PRIO is 1 for the non-boost case. > > Good point! ÂBruno, Sedat, could you please set CONFIG_RCU_BOOST_PRIO to > (say) 50, and see if this still happens? Â(I bet that you do, but...) > What's with CONFIG_RCU_BOOST_DELAY setting? Are those values OK? $ egrep 'M486|M686|X86_UP|CONFIG_SMP|NR_CPUS|PREEMPT|_RCU|_HIGHMEM|PAE' .config CONFIG_TREE_PREEMPT_RCU=y CONFIG_PREEMPT_RCU=y CONFIG_RCU_TRACE=y CONFIG_RCU_FANOUT=32 # CONFIG_RCU_FANOUT_EXACT is not set CONFIG_TREE_RCU_TRACE=y CONFIG_RCU_BOOST=y CONFIG_RCU_BOOST_PRIO=50 CONFIG_RCU_BOOST_DELAY=500 CONFIG_SMP=y # CONFIG_M486 is not set CONFIG_M686=y CONFIG_NR_CPUS=32 # CONFIG_PREEMPT_NONE is not set # CONFIG_PREEMPT_VOLUNTARY is not set CONFIG_PREEMPT=y CONFIG_HIGHMEM4G=y # CONFIG_HIGHMEM64G is not set CONFIG_HIGHMEM=y CONFIG_DEBUG_OBJECTS_RCU_HEAD=y CONFIG_DEBUG_PREEMPT=y # CONFIG_SPARSE_RCU_POINTER is not set # CONFIG_DEBUG_HIGHMEM is not set CONFIG_RCU_TORTURE_TEST=m CONFIG_RCU_CPU_STALL_TIMEOUT=60 CONFIG_RCU_CPU_STALL_VERBOSE=y CONFIG_PREEMPT_TRACER=y - Sedat - >> Is that so low that even the idle thread will take priority? It's a UP >> config with PREEMPT_VOLUNTARY. So pretty much _all_ the stars are >> aligned for odd scheduling behavior. >> >> Other users of SCHED_FIFO tend to set the priority really high (eg >> "MAX_RT_PRIO-1" is clearly the default one - softirq's, watchdog), but >> "1" is not unheard of either (touchscreen/ucb1400_ts and >> mmc/core/sdio_irq), and there are some other random choises out tere. >> >> Any ideas? > > I have found one bug so far in my code, but it only affects TREE_RCU > in my -rcu tree, and even then only if HOTPLUG_CPU is enabled. ÂI am > testing a fix, but I expect Sedat's tests to still break. > > I gave Sedat a patch that make rcu_kthread() run at normal (non-realtime) > priority, and he did not see the failure. ÂSo running non-realtime at > least greatly reduces the probability of failure. > >                            ÂThanx, Paul > -- > To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at Âhttp://vger.kernel.org/majordomo-info.html > -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
