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Date: Tue, 14 Dec 2021 15:19:33 -0800
From: "Paul E. McKenney" <paulmck@...nel.org>
To: kernel test robot <lkp@...el.com>
Cc: kbuild-all@...ts.01.org, linux-kernel@...r.kernel.org
Subject: Re: [paulmck-rcu:rcu/next 27/33] kernel/rcu/tree.c:1180:19: warning:
variable 'rnp' set but not used
On Tue, Dec 14, 2021 at 11:35:51AM +0800, kernel test robot wrote:
> tree: https://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git rcu/next
> head: a4b57ded94e522e2870ae9504f776caa0f615148
> commit: ee418df93691657d27f6118d1ff8f681c52f4aa3 [27/33] rcu: Create and use a rcu_rdp_cpu_online()
> config: i386-randconfig-s001-20211213 (https://download.01.org/0day-ci/archive/20211214/202112141117.jFtY2VyL-lkp@intel.com/config)
> compiler: gcc-9 (Debian 9.3.0-22) 9.3.0
> reproduce:
> # apt-get install sparse
> # sparse version: v0.6.4-dirty
> # https://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git/commit/?id=ee418df93691657d27f6118d1ff8f681c52f4aa3
> git remote add paulmck-rcu https://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git
> git fetch --no-tags paulmck-rcu rcu/next
> git checkout ee418df93691657d27f6118d1ff8f681c52f4aa3
> # save the config file to linux build tree
> mkdir build_dir
> make W=1 C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__' O=build_dir ARCH=i386 SHELL=/bin/bash kernel/rcu/
>
> 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: In function 'rcu_lockdep_current_cpu_online':
> >> kernel/rcu/tree.c:1180:19: warning: variable 'rnp' set but not used [-Wunused-but-set-variable]
> 1180 | struct rcu_node *rnp;
> | ^~~
Good catch, and I am folding the fix into the original commit with
attribution.
Thanx, Paul
> vim +/rnp +1180 kernel/rcu/tree.c
>
> c0d6d01bffdce1 kernel/rcutree.c Paul E. McKenney 2012-01-23 1163
> c0d6d01bffdce1 kernel/rcutree.c Paul E. McKenney 2012-01-23 1164 /*
> 5554788e1d4253 kernel/rcu/tree.c Paul E. McKenney 2018-05-15 1165 * Is the current CPU online as far as RCU is concerned?
> 2036d94a7b61ca kernel/rcutree.c Paul E. McKenney 2012-01-30 1166 *
> 5554788e1d4253 kernel/rcu/tree.c Paul E. McKenney 2018-05-15 1167 * Disable preemption to avoid false positives that could otherwise
> 5554788e1d4253 kernel/rcu/tree.c Paul E. McKenney 2018-05-15 1168 * happen due to the current CPU number being sampled, this task being
> 5554788e1d4253 kernel/rcu/tree.c Paul E. McKenney 2018-05-15 1169 * preempted, its old CPU being taken offline, resuming on some other CPU,
> 49918a54e63c99 kernel/rcu/tree.c Paul E. McKenney 2018-07-07 1170 * then determining that its old CPU is now offline.
> c0d6d01bffdce1 kernel/rcutree.c Paul E. McKenney 2012-01-23 1171 *
> 5554788e1d4253 kernel/rcu/tree.c Paul E. McKenney 2018-05-15 1172 * Disable checking if in an NMI handler because we cannot safely
> 5554788e1d4253 kernel/rcu/tree.c Paul E. McKenney 2018-05-15 1173 * report errors from NMI handlers anyway. In addition, it is OK to use
> 5554788e1d4253 kernel/rcu/tree.c Paul E. McKenney 2018-05-15 1174 * RCU on an offline processor during initial boot, hence the check for
> 5554788e1d4253 kernel/rcu/tree.c Paul E. McKenney 2018-05-15 1175 * rcu_scheduler_fully_active.
> c0d6d01bffdce1 kernel/rcutree.c Paul E. McKenney 2012-01-23 1176 */
> c0d6d01bffdce1 kernel/rcutree.c Paul E. McKenney 2012-01-23 1177 bool rcu_lockdep_current_cpu_online(void)
> c0d6d01bffdce1 kernel/rcutree.c Paul E. McKenney 2012-01-23 1178 {
> 2036d94a7b61ca kernel/rcutree.c Paul E. McKenney 2012-01-30 1179 struct rcu_data *rdp;
> 2036d94a7b61ca kernel/rcutree.c Paul E. McKenney 2012-01-30 @1180 struct rcu_node *rnp;
> b97d23c51c9fee kernel/rcu/tree.c Paul E. McKenney 2018-07-04 1181 bool ret = false;
> c0d6d01bffdce1 kernel/rcutree.c Paul E. McKenney 2012-01-23 1182
> 5554788e1d4253 kernel/rcu/tree.c Paul E. McKenney 2018-05-15 1183 if (in_nmi() || !rcu_scheduler_fully_active)
> f6f7ee9af7554e kernel/rcu/tree.c Fengguang Wu 2013-10-10 1184 return true;
> ff5c4f5cad3306 kernel/rcu/tree.c Thomas Gleixner 2020-03-13 1185 preempt_disable_notrace();
> da1df50d16171f kernel/rcu/tree.c Paul E. McKenney 2018-07-03 1186 rdp = this_cpu_ptr(&rcu_data);
> 2036d94a7b61ca kernel/rcutree.c Paul E. McKenney 2012-01-30 1187 rnp = rdp->mynode;
> defd1f8a1f4efe kernel/rcu/tree.c David Woodhouse 2021-02-16 1188 /*
> defd1f8a1f4efe kernel/rcu/tree.c David Woodhouse 2021-02-16 1189 * Strictly, we care here about the case where the current CPU is
> defd1f8a1f4efe kernel/rcu/tree.c David Woodhouse 2021-02-16 1190 * in rcu_cpu_starting() and thus has an excuse for rdp->grpmask
> defd1f8a1f4efe kernel/rcu/tree.c David Woodhouse 2021-02-16 1191 * not being up to date. So arch_spin_is_locked() might have a
> defd1f8a1f4efe kernel/rcu/tree.c David Woodhouse 2021-02-16 1192 * false positive if it's held by some *other* CPU, but that's
> defd1f8a1f4efe kernel/rcu/tree.c David Woodhouse 2021-02-16 1193 * OK because that just means a false *negative* on the warning.
> defd1f8a1f4efe kernel/rcu/tree.c David Woodhouse 2021-02-16 1194 */
> ee418df9369165 kernel/rcu/tree.c Paul E. McKenney 2021-12-10 1195 if (rcu_rdp_cpu_online(rdp) || arch_spin_is_locked(&rcu_state.ofl_lock))
> b97d23c51c9fee kernel/rcu/tree.c Paul E. McKenney 2018-07-04 1196 ret = true;
> ff5c4f5cad3306 kernel/rcu/tree.c Thomas Gleixner 2020-03-13 1197 preempt_enable_notrace();
> b97d23c51c9fee kernel/rcu/tree.c Paul E. McKenney 2018-07-04 1198 return ret;
> c0d6d01bffdce1 kernel/rcutree.c Paul E. McKenney 2012-01-23 1199 }
> c0d6d01bffdce1 kernel/rcutree.c Paul E. McKenney 2012-01-23 1200 EXPORT_SYMBOL_GPL(rcu_lockdep_current_cpu_online);
> c0d6d01bffdce1 kernel/rcutree.c Paul E. McKenney 2012-01-23 1201
>
> :::::: The code at line 1180 was first introduced by commit
> :::::: 2036d94a7b61ca5032ce90f2bda06afec0fe713e rcu: Rework detection of use of RCU by offline CPUs
>
> :::::: TO: Paul E. McKenney <paul.mckenney@...aro.org>
> :::::: 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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