From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail144.messagelabs.com (mail144.messagelabs.com [216.82.254.51]) by kanga.kvack.org (Postfix) with ESMTP id 455D99000C1 for ; Tue, 26 Apr 2011 14:50:48 -0400 (EDT) Received: from d01relay01.pok.ibm.com (d01relay01.pok.ibm.com [9.56.227.233]) by e4.ny.us.ibm.com (8.14.4/8.13.1) with ESMTP id p3QIUJoh003673 for ; Tue, 26 Apr 2011 14:30:19 -0400 Received: from d01av01.pok.ibm.com (d01av01.pok.ibm.com [9.56.224.215]) by d01relay01.pok.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id p3QIoeMc039530 for ; Tue, 26 Apr 2011 14:50:40 -0400 Received: from d01av01.pok.ibm.com (loopback [127.0.0.1]) by d01av01.pok.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id p3QIodpq026312 for ; Tue, 26 Apr 2011 14:50:40 -0400 Date: Tue, 26 Apr 2011 11:50:36 -0700 From: "Paul E. McKenney" Subject: Re: 2.6.39-rc4+: Kernel leaking memory during FS scanning, regression? Message-ID: <20110426185036.GG2135@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20110425203606.4e78246c@neptune.home> <20110425191607.GL2468@linux.vnet.ibm.com> <20110425231016.34b4293e@neptune.home> <20110425214933.GO2468@linux.vnet.ibm.com> <20110426081904.0d2b1494@pluto.restena.lu> <20110426112756.GF4308@linux.vnet.ibm.com> <20110426183859.6ff6279b@neptune.home> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: Linus Torvalds Cc: Bruno =?iso-8859-1?Q?Pr=E9mont?= , Ingo Molnar , Peter Zijlstra , Mike Frysinger , KOSAKI Motohiro , linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, "Paul E. McKenney" , Pekka Enberg On Tue, Apr 26, 2011 at 10:12:39AM -0700, Linus Torvalds wrote: > On Tue, Apr 26, 2011 at 9:38 AM, Bruno Premont > wrote: > > > > Here it comes: > > > > rcu_kthread (when build processes are STOPped): > > [ 836.050003] rcu_kthread R running 7324 6 2 0x00000000 > > [ 836.050003] dd473f28 00000046 5a000240 dd65207c dd407360 dd651d40 0000035c dd473ed8 > > [ 836.050003] c10bf8a2 c14d63d8 dd65207c dd473f28 dd445040 dd445040 dd473eec c10be848 > > [ 836.050003] dd651d40 dd407360 ddfdca00 dd473f14 c10bfde2 00000000 00000001 000007b6 > > [ 836.050003] Call Trace: > > [ 836.050003] [] ? check_object+0x92/0x210 > > [ 836.050003] [] ? init_object+0x38/0x70 > > [ 836.050003] [] ? free_debug_processing+0x112/0x1f0 > > [ 836.050003] [] ? lock_timer_base+0x2d/0x70 > > [ 836.050003] [] 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. TINY_RCU switched to a kthread when I implemented RCU priority boosting. There 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. Which 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! Bruno, Sedat, could you please set CONFIG_RCU_BOOST_PRIO to (say) 50, and see if this still happens? (I bet that you do, but...) > 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. I 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. So running non-realtime at least greatly reduces the probability of failure. Thanx, Paul -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org