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Date: Mon, 13 Dec 2021 16:36:36 +0800
From: "Chen, Rong A" <rong.a.chen@...el.com>
To: paulmck@...nel.org, kernel test robot <lkp@...el.com>
Cc: David Woodhouse <dwmw@...zon.co.uk>, llvm@...ts.linux.dev,
kbuild-all@...ts.01.org, linux-kernel@...r.kernel.org
Subject: Re: [kbuild-all] Re: [paulmck-rcu:dev.2021.12.07a 56/57]
kernel/rcu/tree.c:4312:45: warning: variable 'flags' is uninitialized when
used here
On 12/10/2021 9:57 PM, Paul E. McKenney wrote:
> On Fri, Dec 10, 2021 at 03:30:22PM +0800, kernel test robot wrote:
>> tree: https://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git dev.2021.12.07a
>> head: 89ddc546d3ad541bc89ec553c92036c98aef57a6
>> commit: 342f2d0f88f3c2d7ab2ae206be5846579319e3bf [56/57] rcu: Kill rnp->ofl_seq and use only rcu_state.ofl_lock for exclusion
>> config: hexagon-randconfig-r041-20211210 (https://download.01.org/0day-ci/archive/20211210/202112101543.wHvqhgYk-lkp@intel.com/config)
>> compiler: clang version 14.0.0 (https://github.com/llvm/llvm-project 097a1cb1d5ebb3a0ec4bcaed8ba3ff6a8e33c00a)
>> reproduce (this is a W=1 build):
>> wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
>> chmod +x ~/bin/make.cross
>> # https://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git/commit/?id=342f2d0f88f3c2d7ab2ae206be5846579319e3bf
>> git remote add paulmck-rcu https://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git
>> git fetch --no-tags paulmck-rcu dev.2021.12.07a
>> git checkout 342f2d0f88f3c2d7ab2ae206be5846579319e3bf
>> # save the config file to linux build tree
>> mkdir build_dir
>> COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross W=1 O=build_dir ARCH=hexagon SHELL=/bin/bash
>>
>> If you fix the issue, kindly add following tag as appropriate
>> Reported-by: kernel test robot <lkp@...el.com>
>>
>> All warnings (new ones prefixed by >>):
>>
>>>> kernel/rcu/tree.c:4312:45: warning: variable 'flags' is uninitialized when used here [-Wuninitialized]
>> rcu_report_qs_rnp(mask, rnp, rnp->gp_seq, flags);
>> ^~~~~
>> kernel/rcu/tree.c:4280:21: note: initialize the variable 'flags' to silence this warning
>> unsigned long flags, seq_flags;
>> ^
>> = 0
>> 1 warning generated.
>
> Good catch, but Neeraj and David beat you to this. The updated commit
> is defd1f8a1f4e ("rcu: Kill rnp->ofl_seq and use only rcu_state.ofl_lock
> for exclusion").
>
> One thing that might be helpful to you during times of backlock... In the
> -rcu tree, if you have several branches with the same prefix (for example,
> dev.2021.12.03a, dev.2021.12.07a, and dev.2021.12.09a), you can safely
> ignore all but the last one in lexicographic order. In this example,
> dev.2021.12.09a obsoletes dev.2021.12.03a and dev.2021.12.07a, so you
> would lose nothing by just ignoring the earlier two branches.
>
> Thanx, Paul
Hi Paul,
Thanks for the advice, We'll investigate it in the near future to avoid
sending old issues that already fixed in the latest branch.
Best Regards,
Rong Chen
>
>> vim +/flags +4312 kernel/rcu/tree.c
>>
>> 4df8374254ea929 Thomas Gleixner 2016-07-13 4266
>> 7ec99de36f40261 Paul E. McKenney 2016-06-30 4267 /*
>> 7ec99de36f40261 Paul E. McKenney 2016-06-30 4268 * Mark the specified CPU as being online so that subsequent grace periods
>> 7ec99de36f40261 Paul E. McKenney 2016-06-30 4269 * (both expedited and normal) will wait on it. Note that this means that
>> 7ec99de36f40261 Paul E. McKenney 2016-06-30 4270 * incoming CPUs are not allowed to use RCU read-side critical sections
>> 7ec99de36f40261 Paul E. McKenney 2016-06-30 4271 * until this function is called. Failing to observe this restriction
>> 7ec99de36f40261 Paul E. McKenney 2016-06-30 4272 * will result in lockdep splats.
>> deb34f364398083 Paul E. McKenney 2017-03-23 4273 *
>> deb34f364398083 Paul E. McKenney 2017-03-23 4274 * Note that this function is special in that it is invoked directly
>> deb34f364398083 Paul E. McKenney 2017-03-23 4275 * from the incoming CPU rather than from the cpuhp_step mechanism.
>> deb34f364398083 Paul E. McKenney 2017-03-23 4276 * This is because this function must be invoked at a precise location.
>> 7ec99de36f40261 Paul E. McKenney 2016-06-30 4277 */
>> 7ec99de36f40261 Paul E. McKenney 2016-06-30 4278 void rcu_cpu_starting(unsigned int cpu)
>> 7ec99de36f40261 Paul E. McKenney 2016-06-30 4279 {
>> 342f2d0f88f3c2d David Woodhouse 2021-12-09 4280 unsigned long flags, seq_flags;
>> 7ec99de36f40261 Paul E. McKenney 2016-06-30 4281 unsigned long mask;
>> 7ec99de36f40261 Paul E. McKenney 2016-06-30 4282 struct rcu_data *rdp;
>> 7ec99de36f40261 Paul E. McKenney 2016-06-30 4283 struct rcu_node *rnp;
>> abfce0414814149 Wei Yang 2020-04-19 4284 bool newcpu;
>> 7ec99de36f40261 Paul E. McKenney 2016-06-30 4285
>> c0f97f20e5d97a1 Paul E. McKenney 2020-07-24 4286 rdp = per_cpu_ptr(&rcu_data, cpu);
>> c0f97f20e5d97a1 Paul E. McKenney 2020-07-24 4287 if (rdp->cpu_started)
>> f64c6013a202931 Peter Zijlstra 2018-05-22 4288 return;
>> c0f97f20e5d97a1 Paul E. McKenney 2020-07-24 4289 rdp->cpu_started = true;
>> f64c6013a202931 Peter Zijlstra 2018-05-22 4290
>> 7ec99de36f40261 Paul E. McKenney 2016-06-30 4291 rnp = rdp->mynode;
>> 7ec99de36f40261 Paul E. McKenney 2016-06-30 4292 mask = rdp->grpmask;
>> 342f2d0f88f3c2d David Woodhouse 2021-12-09 4293 local_irq_save(seq_flags);
>> 342f2d0f88f3c2d David Woodhouse 2021-12-09 4294 arch_spin_lock(&rcu_state.ofl_lock);
>> 2caebefb00f03b5 Paul E. McKenney 2021-07-28 4295 rcu_dynticks_eqs_online();
>> 4d60b475f858ebd Paul E. McKenney 2020-10-13 4296 smp_mb(); // Pair with rcu_gp_cleanup()'s ->ofl_seq barrier().
>> 342f2d0f88f3c2d David Woodhouse 2021-12-09 4297 raw_spin_lock_rcu_node(rnp);
>> 105abf82b0a6266 Paul E. McKenney 2020-01-03 4298 WRITE_ONCE(rnp->qsmaskinitnext, rnp->qsmaskinitnext | mask);
>> abfce0414814149 Wei Yang 2020-04-19 4299 newcpu = !(rnp->expmaskinitnext & mask);
>> 7ec99de36f40261 Paul E. McKenney 2016-06-30 4300 rnp->expmaskinitnext |= mask;
>> 313517fc44fb2d8 Paul E. McKenney 2017-06-08 4301 /* Allow lockless access for expedited grace periods. */
>> abfce0414814149 Wei Yang 2020-04-19 4302 smp_store_release(&rcu_state.ncpus, rcu_state.ncpus + newcpu); /* ^^^ */
>> 2f08469563550d1 Paul E. McKenney 2020-02-10 4303 ASSERT_EXCLUSIVE_WRITER(rcu_state.ncpus);
>> e05121ba5b81e2f Paul E. McKenney 2018-05-07 4304 rcu_gpnum_ovf(rnp, rdp); /* Offline-induced counter wrap? */
>> eb7a6653887b540 Paul E. McKenney 2018-07-05 4305 rdp->rcu_onl_gp_seq = READ_ONCE(rcu_state.gp_seq);
>> eb7a6653887b540 Paul E. McKenney 2018-07-05 4306 rdp->rcu_onl_gp_flags = READ_ONCE(rcu_state.gp_flags);
>> 9f866dac94292f9 Joel Fernandes (Google 2020-09-29 4307)
>> 9f866dac94292f9 Joel Fernandes (Google 2020-09-29 4308) /* An incoming CPU should never be blocking a grace period. */
>> 9f866dac94292f9 Joel Fernandes (Google 2020-09-29 4309) if (WARN_ON_ONCE(rnp->qsmask & mask)) { /* RCU waiting on incoming CPU? */
>> 516e5ae0c940162 Joel Fernandes (Google 2019-09-05 4310) rcu_disable_urgency_upon_qs(rdp);
>> 99990da1b3c00f6 Paul E. McKenney 2018-05-03 4311 /* Report QS -after- changing ->qsmaskinitnext! */
>> b50912d0b5e03f1 Paul E. McKenney 2018-07-03 @4312 rcu_report_qs_rnp(mask, rnp, rnp->gp_seq, flags);
>> 99990da1b3c00f6 Paul E. McKenney 2018-05-03 4313 } else {
>> 7ec99de36f40261 Paul E. McKenney 2016-06-30 4314 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
>> 7ec99de36f40261 Paul E. McKenney 2016-06-30 4315 }
>> 342f2d0f88f3c2d David Woodhouse 2021-12-09 4316 arch_spin_unlock(&rcu_state.ofl_lock);
>> 342f2d0f88f3c2d David Woodhouse 2021-12-09 4317 local_irq_restore(seq_flags);
>> 313517fc44fb2d8 Paul E. McKenney 2017-06-08 4318 smp_mb(); /* Ensure RCU read-side usage follows above initialization. */
>> 7ec99de36f40261 Paul E. McKenney 2016-06-30 4319 }
>> 7ec99de36f40261 Paul E. McKenney 2016-06-30 4320
>>
>> :::::: The code at line 4312 was first introduced by commit
>> :::::: b50912d0b5e03f11004fec1e2b50244de9e2fa41 rcu: Remove rsp parameter from rcu_report_qs_rnp()
>>
>> :::::: TO: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
>> :::::: CC: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
>>
>> ---
>> 0-DAY CI Kernel Test Service, Intel Corporation
>> https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org
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