[ammarfaizi2-block:paulmck/linux-rcu/dev 77/78] kernel/rcu/tasks.h:1231:12: warning: variable 'realnew' set but not used

[kernel test robot <lkp@intel.com>]

tree:   https://github.com/ammarfaizi2/linux-block paulmck/linux-rcu/dev
head:   19abca3f9f9095e58c46e2f169543705bd92cf35
commit: 4b3564b0807387c66b80b24095019479584039c9 [77/78] rcu-tasks: Manual revert of 4b2a6af8fe31e85fb2754b8da5072041a4dea471
config: m68k-defconfig (https://download.01.org/0day-ci/archive/20220601/202206011656.3Ab9OjRb-lkp@intel.com/config)
compiler: m68k-linux-gcc (GCC) 11.3.0
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/4b3564b0807387c66b80b24095019479584039c9
        git remote add ammarfaizi2-block https://github.com/ammarfaizi2/linux-block
        git fetch --no-tags ammarfaizi2-block paulmck/linux-rcu/dev
        git checkout 4b3564b0807387c66b80b24095019479584039c9
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-11.3.0 make.cross W=1 O=build_dir ARCH=m68k SHELL=/bin/bash kernel/

If you fix the issue, kindly add following tag where applicable
Reported-by: kernel test robot <lkp@intel.com>

All warnings (new ones prefixed by >>):

   In file included from kernel/rcu/update.c:606:
   kernel/rcu/tasks.h: In function 'rcu_trc_cmpxchg_need_qs':
   kernel/rcu/tasks.h:1239:9: error: aggregate value used where an integer was expected
    1239 |         ret = cmpxchg(&t->trc_reader_special, trs_old, trs_new);
         |         ^~~
   kernel/rcu/tasks.h:1239:9: error: aggregate value used where an integer was expected
   In file included from arch/m68k/include/asm/cmpxchg.h:131,
                    from arch/m68k/include/asm/atomic.h:7,
                    from include/linux/atomic.h:7,
                    from include/linux/cpumask.h:13,
                    from include/linux/smp.h:13,
                    from include/linux/lockdep.h:14,
                    from include/linux/spinlock.h:62,
                    from kernel/rcu/update.c:23:
   include/asm-generic/cmpxchg.h:92:10: error: cast to union type from type not present in union
      92 |         ((__typeof__(*(ptr)))__generic_cmpxchg_local((ptr), (unsigned long)(o), \
         |          ^
   include/asm-generic/cmpxchg.h:105:33: note: in expansion of macro 'generic_cmpxchg_local'
     105 | #define arch_cmpxchg_local      generic_cmpxchg_local
         |                                 ^~~~~~~~~~~~~~~~~~~~~
   include/asm-generic/cmpxchg.h:112:33: note: in expansion of macro 'arch_cmpxchg_local'
     112 | #define arch_cmpxchg            arch_cmpxchg_local
         |                                 ^~~~~~~~~~~~~~~~~~
   include/linux/atomic/atomic-instrumented.h:1916:9: note: in expansion of macro 'arch_cmpxchg'
    1916 |         arch_cmpxchg(__ai_ptr, __VA_ARGS__); \
         |         ^~~~~~~~~~~~
   kernel/rcu/tasks.h:1239:15: note: in expansion of macro 'cmpxchg'
    1239 |         ret = cmpxchg(&t->trc_reader_special, trs_old, trs_new);
         |               ^~~~~~~
   In file included from kernel/rcu/update.c:606:
>> kernel/rcu/tasks.h:1231:12: warning: variable 'realnew' set but not used [-Wunused-but-set-variable]
    1231 |         u8 realnew;
         |            ^~~~~~~


vim +/realnew +1231 kernel/rcu/tasks.h

122db3cac94c0b Paul E. McKenney 2022-05-23  1223  
0f7cb0c989a98c Paul E. McKenney 2022-05-24  1224  /*
0f7cb0c989a98c Paul E. McKenney 2022-05-24  1225   * Do a cmpxchg() on ->trc_reader_special.b.need_qs, allowing for
0f7cb0c989a98c Paul E. McKenney 2022-05-24  1226   * the four-byte operand-size restriction of some platforms.
0f7cb0c989a98c Paul E. McKenney 2022-05-24  1227   * Returns the old value, which is often ignored.
0f7cb0c989a98c Paul E. McKenney 2022-05-24  1228   */
0f7cb0c989a98c Paul E. McKenney 2022-05-24  1229  u8 rcu_trc_cmpxchg_need_qs(struct task_struct *t, u8 old, u8 new)
0f7cb0c989a98c Paul E. McKenney 2022-05-24  1230  {
2b23adb3446ac4 Paul E. McKenney 2022-05-25 @1231  	u8 realnew;
2b23adb3446ac4 Paul E. McKenney 2022-05-25  1232  	union rcu_special ret;
0f7cb0c989a98c Paul E. McKenney 2022-05-24  1233  	union rcu_special trs_old = READ_ONCE(t->trc_reader_special);
0f7cb0c989a98c Paul E. McKenney 2022-05-24  1234  	union rcu_special trs_new = trs_old;
0f7cb0c989a98c Paul E. McKenney 2022-05-24  1235  
0f7cb0c989a98c Paul E. McKenney 2022-05-24  1236  	if (trs_old.b.need_qs != old)
0f7cb0c989a98c Paul E. McKenney 2022-05-24  1237  		return trs_old.b.need_qs;
0f7cb0c989a98c Paul E. McKenney 2022-05-24  1238  	trs_new.b.need_qs = new;
2b23adb3446ac4 Paul E. McKenney 2022-05-25  1239  	ret = cmpxchg(&t->trc_reader_special, trs_old, trs_new);
2b23adb3446ac4 Paul E. McKenney 2022-05-25  1240  	realnew = READ_ONCE(t->trc_reader_special.b.need_qs);
2b23adb3446ac4 Paul E. McKenney 2022-05-25  1241  	return ret.b.need_qs;
0f7cb0c989a98c Paul E. McKenney 2022-05-24  1242  }
0f7cb0c989a98c Paul E. McKenney 2022-05-24  1243  

:::::: The code at line 1231 was first introduced by commit
:::::: 2b23adb3446ac4098c17dee98414df6fca07f6c9 squash! rcu-tasks: Atomically update .b.need_qs to obviate count

:::::: TO: Paul E. McKenney <paulmck@kernel.org>
:::::: CC: Paul E. McKenney <paulmck@kernel.org>

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