[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 Fri, Dec 10, 2021 at 03:30:22PM +0800, kernel test robot wrote: 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 > 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(a)linux.vnet.ibm.com&gt; > :::::: CC: Paul E. McKenney <paulmck(a)linux.vnet.ibm.com&gt; > > --- > 0-DAY CI Kernel Test Service, Intel Corporation > https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org