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Message-ID: <20130612141457.GA25556@localhost> Date: Wed, 12 Jun 2013 22:14:57 +0800 From: Fengguang Wu <fengguang.wu@...el.com> To: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> Cc: linux-kernel@...r.kernel.org Subject: Re: WARNING: at kernel/rcutorture.c:1243 rcu_torture_printk On Wed, Jun 12, 2013 at 06:48:35AM -0700, Paul E. McKenney wrote: > On Tue, Jun 11, 2013 at 04:37:25PM -0700, Paul E. McKenney wrote: > > On Tue, Jun 11, 2013 at 04:03:22PM -0700, Paul E. McKenney wrote: > > > On Tue, Jun 11, 2013 at 10:14:55AM +0800, Fengguang Wu wrote: > > > > Paul, > > > > > > > > On Mon, Jun 10, 2013 at 07:51:10AM -0700, Paul E. McKenney wrote: > > > > > On Mon, Jun 10, 2013 at 03:47:28PM +0800, Fengguang Wu wrote: > > > > > > Greetings, > > > > > > > > > > > > I got the below dmesg and the first bad commit is > > > > > > > > > > > > commit 911af505ef407c2511106c224dd640f882f0f590 > > > > > > Author: Paul E. McKenney <paul.mckenney@...aro.org> > > > > > > Date: Mon Feb 11 10:23:27 2013 -0800 > > > > > > > > > > > > rcu: Provide compile-time control for no-CBs CPUs > > > > > > > > > > > > Currently, the only way to specify no-CBs CPUs is via the rcu_nocbs > > > > > > kernel command-line parameter. This is inconvenient in some cases, > > > > > > particularly for randconfig testing, so this commit adds a new set of > > > > > > kernel configuration parameters. CONFIG_RCU_NOCB_CPU_NONE (the default) > > > > > > retains the old behavior, CONFIG_RCU_NOCB_CPU_ZERO offloads callback > > > > > > processing from CPU 0 (along with any other CPUs specified by the > > > > > > rcu_nocbs boot-time parameter), and CONFIG_RCU_NOCB_CPU_ALL offloads > > > > > > callback processing from all CPUs. > > > > > > > > > > > > Signed-off-by: Paul E. McKenney <paul.mckenney@...aro.org> > > > > > > Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com> > > > > > > > > > > > > However I guess it's a wrong bisect, the commit should be unmasking an > > > > > > old bug because it merely provides more kconfig options. > > > > > > > > > > > > This warning happened only once in 74 boots of the kernel. > > > > > > > > > > > > I also attached the 2nd dmesg which shows boot hang for the same > > > > > > kernel. > > > > > > > > > > > > Note that there are also 2 kernel hangs in the 74 boots. It should > > > > > > not be an RCU problem, however for completeness, I also attach a dmesg > > > > > > for your reference when considering this RCU warning. > > > > > > > > > > Either way, that is a nasty warning! You get this on recent kernels as > > > > > well, I take it? > > > > > > > > Yes, the warning is still in recent kernels, indicated from the last > > > > lines of the bisect log. > > > > > > > > 911af505ef407c2511106c224dd640f882f0f590 is bad and its parent > > > > 34ed62461ae4970695974afb9a60ac3df0086830 is good: > > > > > > git bisect bad 911af505ef407c2511106c224dd640f882f0f590 # 65 2013-06-07 16:14:41 rcu: Provide compile-time control for no-CBs CPUs > > > > > > git bisect good 34ed62461ae4970695974afb9a60ac3df0086830 # 900 2013-06-08 04:57:34 rcu: Remove restrictions on no-CBs CPUs > > > > > > > > After bisect, the script tries to confirm that > > > > 34ed62461ae4970695974afb9a60ac3df0086830 is really good by boot > > > > testing it 2700 more times: > > > > > > > > > > git bisect good 34ed62461ae4970695974afb9a60ac3df0086830 # 2700 2013-06-10 14:33:56 rcu: Remove restrictions on no-CBs CPUs > > > > > > > > And continue to find out whether the linus/master and > > > > linux-next/master are good/bad (here the results are both bad): > > > > > > > > > > git bisect bad f43e7a34255a387930bc2bb826ec17c052ce975e # 14:34 0 Merge branch 'for-next' > > > > > > git bisect bad c04efed734409f5a44715b54a6ca1b54b0ccf215 # 14:41 11 Add linux-next specific files for 20130607 > > > > > > Just to let you know that I am putting some time into this... > > > > > > Well, I got a panic, but it turned out to be the kernel being unable to > > > locate init. Why your .config should have this effect, I have no idea -- > > > I don't see any Kconfig parameters that look to me like they should be > > > specifying where init lives. Any hints? I run randconfig kernels and a smallish ubuntu-core initrd as rootfs. This must be rare setup and may well trigger weird problems. ;) > > > Left to myself, my next step will be to try just the RCU-related Kconfig > > > parameters. > > > > Which gets rid of the "unable to locate init" panic. One strange thing > > in your .config: > > > > CONFIG_HZ_PERIODIC=y > > # CONFIG_NO_HZ_IDLE is not set > > # CONFIG_NO_HZ_FULL is not set > > CONFIG_NO_HZ=y > > > > Seems harmless, though. > > > > I will do repeated runs with this config fragment to see if I can reproduce > > your warning: > > > > CONFIG_TREE_PREEMPT_RCU=y > > CONFIG_PREEMPT_RCU=y > > CONFIG_RCU_STALL_COMMON=y > > CONFIG_RCU_USER_QS=n > > CONFIG_RCU_FANOUT=64 > > CONFIG_RCU_FANOUT_LEAF=16 > > CONFIG_RCU_FANOUT_EXACT=n > > CONFIG_RCU_BOOST=y > > CONFIG_RCU_BOOST_PRIO=1 > > CONFIG_RCU_BOOST_DELAY=500 > > CONFIG_RCU_NOCB_CPU=y > > CONFIG_RCU_NOCB_CPU_NONE=n > > CONFIG_RCU_NOCB_CPU_ZERO=y > > CONFIG_RCU_NOCB_CPU_ALL=n > > CONFIG_DEBUG_OBJECTS_RCU_HEAD=n > > CONFIG_SPARSE_RCU_POINTER=n > > CONFIG_RCU_TORTURE_TEST=y > > CONFIG_RCU_TORTURE_TEST_RUNNABLE=y > > CONFIG_RCU_CPU_STALL_TIMEOUT=21 > > CONFIG_RCU_CPU_STALL_VERBOSE=y > > CONFIG_RCU_CPU_STALL_INFO=y > > CONFIG_RCU_TRACE=n > > CONFIG_NR_CPUS=8 > > CONFIG_HZ_PERIODIC=y > > CONFIG_NO_HZ_IDLE=n > > CONFIG_NO_HZ_FULL=n > > CONFIG_NO_HZ=y > > CONFIG_PREEMPT_NONE=n > > CONFIG_PREEMPT_VOLUNTARY=n > > CONFIG_PREEMPT=y > > CONFIG_PREEMPT_COUNT=y > > And my system completed 200 boots with two minutes of rcutorture without > failure. Any thoughts on what I should try next? Thanks for looking into this and testing it out! I just kicked off a new bisect and hope to collect more information about it. Thanks, Fengguang -- 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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