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Date: Tue, 25 Jan 2022 11:01:42 -0800
From: "Paul E. McKenney" <paulmck@...nel.org>
To: kernel test robot <lkp@...el.com>
Cc: kbuild-all@...ts.01.org, GNU/Weeb Mailing List <gwml@...weeb.org>,
linux-kernel@...r.kernel.org
Subject: Re: [ammarfaizi2-block:paulmck/linux-rcu/dev 80/85]
kernel/rcu/srcutree.c:1168:27: warning: variable 'sdp' set but not used
On Tue, Jan 25, 2022 at 07:24:14PM +0800, kernel test robot wrote:
> tree: https://github.com/ammarfaizi2/linux-block paulmck/linux-rcu/dev
> head: 3cd375aa70d563fe8aa3e5f03280bdd8a334de45
> commit: 2c773bcaf4dd5031d0b2c980cc623ecfbcc6ab62 [80/85] squash! srcu: Make Tree SRCU able to operate without snp_node array
> config: nds32-defconfig (https://download.01.org/0day-ci/archive/20220125/202201251933.iaAyduWp-lkp@intel.com/config)
> compiler: nds32le-linux-gcc (GCC) 11.2.0
> 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://github.com/ammarfaizi2/linux-block/commit/2c773bcaf4dd5031d0b2c980cc623ecfbcc6ab62
> git remote add ammarfaizi2-block https://github.com/ammarfaizi2/linux-block
> git fetch --no-tags ammarfaizi2-block paulmck/linux-rcu/dev
> git checkout 2c773bcaf4dd5031d0b2c980cc623ecfbcc6ab62
> # save the config file to linux build tree
> mkdir build_dir
> COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-11.2.0 make.cross O=build_dir ARCH=nds32 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/srcutree.c: In function 'srcu_barrier':
> >> kernel/rcu/srcutree.c:1168:27: warning: variable 'sdp' set but not used [-Wunused-but-set-variable]
> 1168 | struct srcu_data *sdp;
> | ^~~
Fixed in e3ec4a4e8733 ("srcu: Make Tree SRCU able to operate without
snp_node array").
Thank you for your testing efforts!
Thanx, Paul
> vim +/sdp +1168 kernel/rcu/srcutree.c
>
> 2c773bcaf4dd50 Paul E. McKenney 2022-01-24 1160
> dad81a2026841b Paul E. McKenney 2017-03-25 1161 /**
> dad81a2026841b Paul E. McKenney 2017-03-25 1162 * srcu_barrier - Wait until all in-flight call_srcu() callbacks complete.
> aacb5d91ab1bfb Paul E. McKenney 2018-10-28 1163 * @ssp: srcu_struct on which to wait for in-flight callbacks.
> dad81a2026841b Paul E. McKenney 2017-03-25 1164 */
> aacb5d91ab1bfb Paul E. McKenney 2018-10-28 1165 void srcu_barrier(struct srcu_struct *ssp)
> dad81a2026841b Paul E. McKenney 2017-03-25 1166 {
> da915ad5cf25b5 Paul E. McKenney 2017-04-05 1167 int cpu;
> da915ad5cf25b5 Paul E. McKenney 2017-04-05 @1168 struct srcu_data *sdp;
> aacb5d91ab1bfb Paul E. McKenney 2018-10-28 1169 unsigned long s = rcu_seq_snap(&ssp->srcu_barrier_seq);
> da915ad5cf25b5 Paul E. McKenney 2017-04-05 1170
> aacb5d91ab1bfb Paul E. McKenney 2018-10-28 1171 check_init_srcu_struct(ssp);
> aacb5d91ab1bfb Paul E. McKenney 2018-10-28 1172 mutex_lock(&ssp->srcu_barrier_mutex);
> aacb5d91ab1bfb Paul E. McKenney 2018-10-28 1173 if (rcu_seq_done(&ssp->srcu_barrier_seq, s)) {
> da915ad5cf25b5 Paul E. McKenney 2017-04-05 1174 smp_mb(); /* Force ordering following return. */
> aacb5d91ab1bfb Paul E. McKenney 2018-10-28 1175 mutex_unlock(&ssp->srcu_barrier_mutex);
> da915ad5cf25b5 Paul E. McKenney 2017-04-05 1176 return; /* Someone else did our work for us. */
> da915ad5cf25b5 Paul E. McKenney 2017-04-05 1177 }
> aacb5d91ab1bfb Paul E. McKenney 2018-10-28 1178 rcu_seq_start(&ssp->srcu_barrier_seq);
> aacb5d91ab1bfb Paul E. McKenney 2018-10-28 1179 init_completion(&ssp->srcu_barrier_completion);
> da915ad5cf25b5 Paul E. McKenney 2017-04-05 1180
> da915ad5cf25b5 Paul E. McKenney 2017-04-05 1181 /* Initial count prevents reaching zero until all CBs are posted. */
> aacb5d91ab1bfb Paul E. McKenney 2018-10-28 1182 atomic_set(&ssp->srcu_barrier_cpu_cnt, 1);
> da915ad5cf25b5 Paul E. McKenney 2017-04-05 1183
> 2c773bcaf4dd50 Paul E. McKenney 2022-01-24 1184 if (!smp_load_acquire(&ssp->srcu_size_state)) {
> 2c773bcaf4dd50 Paul E. McKenney 2022-01-24 1185 srcu_barrier_one_cpu(ssp, per_cpu_ptr(ssp->sda, 0));
> 2c773bcaf4dd50 Paul E. McKenney 2022-01-24 1186 } else {
> 2c773bcaf4dd50 Paul E. McKenney 2022-01-24 1187
> da915ad5cf25b5 Paul E. McKenney 2017-04-05 1188 /*
> da915ad5cf25b5 Paul E. McKenney 2017-04-05 1189 * Each pass through this loop enqueues a callback, but only
> da915ad5cf25b5 Paul E. McKenney 2017-04-05 1190 * on CPUs already having callbacks enqueued. Note that if
> da915ad5cf25b5 Paul E. McKenney 2017-04-05 1191 * a CPU already has callbacks enqueue, it must have already
> da915ad5cf25b5 Paul E. McKenney 2017-04-05 1192 * registered the need for a future grace period, so all we
> da915ad5cf25b5 Paul E. McKenney 2017-04-05 1193 * need do is enqueue a callback that will use the same
> da915ad5cf25b5 Paul E. McKenney 2017-04-05 1194 * grace period as the last callback already in the queue.
> da915ad5cf25b5 Paul E. McKenney 2017-04-05 1195 */
> da915ad5cf25b5 Paul E. McKenney 2017-04-05 1196 for_each_possible_cpu(cpu) {
> aacb5d91ab1bfb Paul E. McKenney 2018-10-28 1197 sdp = per_cpu_ptr(ssp->sda, cpu);
> 2c773bcaf4dd50 Paul E. McKenney 2022-01-24 1198 srcu_barrier_one_cpu(ssp, per_cpu_ptr(ssp->sda, cpu));
> a602538e46c9c6 Paul E. McKenney 2017-04-28 1199 }
> da915ad5cf25b5 Paul E. McKenney 2017-04-05 1200 }
> da915ad5cf25b5 Paul E. McKenney 2017-04-05 1201
> da915ad5cf25b5 Paul E. McKenney 2017-04-05 1202 /* Remove the initial count, at which point reaching zero can happen. */
> aacb5d91ab1bfb Paul E. McKenney 2018-10-28 1203 if (atomic_dec_and_test(&ssp->srcu_barrier_cpu_cnt))
> aacb5d91ab1bfb Paul E. McKenney 2018-10-28 1204 complete(&ssp->srcu_barrier_completion);
> aacb5d91ab1bfb Paul E. McKenney 2018-10-28 1205 wait_for_completion(&ssp->srcu_barrier_completion);
> da915ad5cf25b5 Paul E. McKenney 2017-04-05 1206
> aacb5d91ab1bfb Paul E. McKenney 2018-10-28 1207 rcu_seq_end(&ssp->srcu_barrier_seq);
> aacb5d91ab1bfb Paul E. McKenney 2018-10-28 1208 mutex_unlock(&ssp->srcu_barrier_mutex);
> dad81a2026841b Paul E. McKenney 2017-03-25 1209 }
> dad81a2026841b Paul E. McKenney 2017-03-25 1210 EXPORT_SYMBOL_GPL(srcu_barrier);
> dad81a2026841b Paul E. McKenney 2017-03-25 1211
>
> :::::: The code at line 1168 was first introduced by commit
> :::::: da915ad5cf25b5f5d358dd3670c3378d8ae8c03e srcu: Parallelize callback handling
>
> :::::: 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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