[paulmck-rcu:dev.2021.12.09b 35/37] kernel/rcu/tree.c:4072:23: warning: variable 'lseq' set but not used
From: kernel test robot
Date: Tue Dec 14 2021 - 21:54:46 EST
tree: https://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git dev.2021.12.09b
head: 0f1825f9df5a83cfeca5f1ecce96633223bf78d2
commit: ca34220fecf856ef7521c912a8812f2c1ea53ab3 [35/37] rcu: Rework rcu_barrier() and callback-migration logic
config: nds32-defconfig (https://download.01.org/0day-ci/archive/20211215/202112151008.JsE9k2En-lkp@xxxxxxxxx/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://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git/commit/?id=ca34220fecf856ef7521c912a8812f2c1ea53ab3
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.2021.12.09b
git checkout ca34220fecf856ef7521c912a8812f2c1ea53ab3
# 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@xxxxxxxxx>
All warnings (new ones prefixed by >>):
kernel/rcu/tree.c: In function 'rcu_barrier':
>> kernel/rcu/tree.c:4072:23: warning: variable 'lseq' set but not used [-Wunused-but-set-variable]
4072 | unsigned long lseq;
| ^~~~
vim +/lseq +4072 kernel/rcu/tree.c
4058
4059 /**
4060 * rcu_barrier - Wait until all in-flight call_rcu() callbacks complete.
4061 *
4062 * Note that this primitive does not necessarily wait for an RCU grace period
4063 * to complete. For example, if there are no RCU callbacks queued anywhere
4064 * in the system, then rcu_barrier() is within its rights to return
4065 * immediately, without waiting for anything, much less an RCU grace period.
4066 */
4067 void rcu_barrier(void)
4068 {
4069 uintptr_t cpu;
4070 unsigned long flags;
4071 unsigned long gseq;
> 4072 unsigned long lseq;
4073 struct rcu_data *rdp;
4074 unsigned long s = rcu_seq_snap(&rcu_state.barrier_sequence);
4075
4076 rcu_barrier_trace(TPS("Begin"), -1, s);
4077
4078 /* Take mutex to serialize concurrent rcu_barrier() requests. */
4079 mutex_lock(&rcu_state.barrier_mutex);
4080
4081 /* Did someone else do our work for us? */
4082 if (rcu_seq_done(&rcu_state.barrier_sequence, s)) {
4083 rcu_barrier_trace(TPS("EarlyExit"), -1, rcu_state.barrier_sequence);
4084 smp_mb(); /* caller's subsequent code after above check. */
4085 mutex_unlock(&rcu_state.barrier_mutex);
4086 return;
4087 }
4088
4089 /* Mark the start of the barrier operation. */
4090 lseq = rcu_state.barrier_sequence;
4091 rcu_seq_start(&rcu_state.barrier_sequence);
4092 gseq = rcu_state.barrier_sequence;
4093 rcu_barrier_trace(TPS("Inc1"), -1, rcu_state.barrier_sequence);
4094
4095 /*
4096 * Initialize the count to two rather than to zero in order
4097 * to avoid a too-soon return to zero in case of an immediate
4098 * invocation of the just-enqueued callback (or preemption of
4099 * this task). Exclude CPU-hotplug operations to ensure that no
4100 * offline non-offloaded CPU has callbacks queued.
4101 */
4102 init_completion(&rcu_state.barrier_completion);
4103 atomic_set(&rcu_state.barrier_cpu_count, 2);
4104 cpus_read_lock();
4105
4106 /*
4107 * Force each CPU with callbacks to register a new callback.
4108 * When that callback is invoked, we will know that all of the
4109 * corresponding CPU's preceding callbacks have been invoked.
4110 */
4111 for_each_possible_cpu(cpu) {
4112 rdp = per_cpu_ptr(&rcu_data, cpu);
4113 retry:
4114 if (READ_ONCE(rdp->barrier_seq_snap) == gseq)
4115 continue;
4116 if (!rcu_segcblist_n_cbs(&rdp->cblist)) {
4117 raw_spin_lock_irqsave(&rdp->barrier_lock, flags);
4118 WRITE_ONCE(rdp->barrier_seq_snap, gseq);
4119 raw_spin_unlock_irqrestore(&rdp->barrier_lock, flags);
4120 rcu_barrier_trace(TPS("NQ"), cpu, rcu_state.barrier_sequence);
4121 continue;
4122 }
4123 if (rcu_rdp_cpu_online(rdp)) {
4124 if (smp_call_function_single(cpu, rcu_barrier_handler, (void *)cpu, 1)) {
4125 schedule_timeout_uninterruptible(1);
4126 goto retry;
4127 }
4128 WARN_ON_ONCE(READ_ONCE(rdp->barrier_seq_snap) != gseq);
4129 rcu_barrier_trace(TPS("OnlineQ"), cpu, rcu_state.barrier_sequence);
4130 continue;
4131 }
4132 if (!rcu_barrier_entrain_if_ofl(rdp)) {
4133 schedule_timeout_uninterruptible(1);
4134 goto retry;
4135 }
4136 WARN_ON_ONCE(READ_ONCE(rdp->barrier_seq_snap) != gseq);
4137 rcu_barrier_trace(TPS("OfflineNoCBQ"), cpu, rcu_state.barrier_sequence);
4138 }
4139 cpus_read_unlock();
4140
4141 /*
4142 * Now that we have an rcu_barrier_callback() callback on each
4143 * CPU, and thus each counted, remove the initial count.
4144 */
4145 if (atomic_sub_and_test(2, &rcu_state.barrier_cpu_count))
4146 complete(&rcu_state.barrier_completion);
4147
4148 /* Wait for all rcu_barrier_callback() callbacks to be invoked. */
4149 wait_for_completion(&rcu_state.barrier_completion);
4150
4151 /* Mark the end of the barrier operation. */
4152 rcu_barrier_trace(TPS("Inc2"), -1, rcu_state.barrier_sequence);
4153 rcu_seq_end(&rcu_state.barrier_sequence);
4154 gseq = rcu_state.barrier_sequence;
4155 for_each_possible_cpu(cpu) {
4156 rdp = per_cpu_ptr(&rcu_data, cpu);
4157
4158 WRITE_ONCE(rdp->barrier_seq_snap, gseq);
4159 }
4160
4161 /* Other rcu_barrier() invocations can now safely proceed. */
4162 mutex_unlock(&rcu_state.barrier_mutex);
4163 }
4164 EXPORT_SYMBOL_GPL(rcu_barrier);
4165
---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/kbuild-all@xxxxxxxxxxxx