linux-kernel - [rcu:test 69/69] arch/x86/include/asm/irqflags.h:41:2: warning: 'flags' may be used uninitialized in this function

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Date:   Fri, 31 May 2019 00:35:01 +0800
From:   kbuild test robot <lkp@...el.com>
To:     "Paul E. McKenney" <paulmck@...ux.ibm.com>
Cc:     kbuild-all@...org, linux-kernel@...r.kernel.org
Subject: [rcu:test 69/69] arch/x86/include/asm/irqflags.h:41:2: warning:
 'flags' may be used uninitialized in this function

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git test
head:   685a26bc60076305987bf06cfd1269e5e4094c73
commit: 685a26bc60076305987bf06cfd1269e5e4094c73 [69/69] rcu/nocb: Avoid ->nocb_lock capture by corresponding CPU
config: x86_64-randconfig-x009-201921 (attached as .config)
compiler: gcc-7 (Debian 7.3.0-1) 7.3.0
reproduce:
        git checkout 685a26bc60076305987bf06cfd1269e5e4094c73
        # save the attached .config to linux build tree
        make ARCH=x86_64 

If you fix the issue, kindly add following tag
Reported-by: kbuild test robot <lkp@...el.com>

Note: it may well be a FALSE warning. FWIW you are at least aware of it now.
http://gcc.gnu.org/wiki/Better_Uninitialized_Warnings

All warnings (new ones prefixed by >>):

   In file included from include/linux/irqflags.h:16:0,
                    from arch/x86/include/asm/processor.h:33,
                    from arch/x86/include/asm/cpufeature.h:5,
                    from arch/x86/include/asm/thread_info.h:53,
                    from include/linux/thread_info.h:38,
                    from arch/x86/include/asm/preempt.h:7,
                    from include/linux/preempt.h:78,
                    from include/linux/spinlock.h:51,
                    from kernel/rcu/tree.c:23:
   kernel/rcu/tree_plugin.h: In function 'rcu_nocb_gp_kthread':
>> arch/x86/include/asm/irqflags.h:41:2: warning: 'flags' may be used uninitialized in this function [-Wmaybe-uninitialized]
     asm volatile("push %0 ; popf"
     ^~~
   In file included from kernel/rcu/tree.c:3519:0:
   kernel/rcu/tree_plugin.h:1719:16: note: 'flags' was declared here
     unsigned long flags;
                   ^~~~~
   kernel/rcu/tree_plugin.h: In function 'do_nocb_deferred_wakeup_common':
   kernel/rcu/tree_plugin.h:1891:2: warning: 'flags' may be used uninitialized in this function [-Wmaybe-uninitialized]
     wake_nocb_gp(rdp, ndw == RCU_NOCB_WAKE_FORCE, flags);
     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--
   In file included from include/linux/irqflags.h:16:0,
                    from arch/x86/include/asm/processor.h:33,
                    from arch/x86/include/asm/cpufeature.h:5,
                    from arch/x86/include/asm/thread_info.h:53,
                    from include/linux/thread_info.h:38,
                    from arch/x86/include/asm/preempt.h:7,
                    from include/linux/preempt.h:78,
                    from include/linux/spinlock.h:51,
                    from kernel//rcu/tree.c:23:
   kernel//rcu/tree_plugin.h: In function 'rcu_nocb_gp_kthread':
>> arch/x86/include/asm/irqflags.h:41:2: warning: 'flags' may be used uninitialized in this function [-Wmaybe-uninitialized]
     asm volatile("push %0 ; popf"
     ^~~
   In file included from kernel//rcu/tree.c:3519:0:
   kernel//rcu/tree_plugin.h:1719:16: note: 'flags' was declared here
     unsigned long flags;
                   ^~~~~
   kernel//rcu/tree_plugin.h: In function 'do_nocb_deferred_wakeup_common':
   kernel//rcu/tree_plugin.h:1891:2: warning: 'flags' may be used uninitialized in this function [-Wmaybe-uninitialized]
     wake_nocb_gp(rdp, ndw == RCU_NOCB_WAKE_FORCE, flags);
     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

vim +/flags +41 arch/x86/include/asm/irqflags.h

6abcd98f include/asm-x86/irqflags.h      Glauber de Oliveira Costa 2008-01-30  37  
1f59a458 arch/x86/include/asm/irqflags.h Nick Desaulniers          2018-08-27  38  extern inline void native_restore_fl(unsigned long flags);
1f59a458 arch/x86/include/asm/irqflags.h Nick Desaulniers          2018-08-27  39  extern inline void native_restore_fl(unsigned long flags)
6abcd98f include/asm-x86/irqflags.h      Glauber de Oliveira Costa 2008-01-30  40  {
cf7f7191 include/asm-x86/irqflags.h      Joe Perches               2008-03-23 @41  	asm volatile("push %0 ; popf"
6abcd98f include/asm-x86/irqflags.h      Glauber de Oliveira Costa 2008-01-30  42  		     : /* no output */
6abcd98f include/asm-x86/irqflags.h      Glauber de Oliveira Costa 2008-01-30  43  		     :"g" (flags)
cf7f7191 include/asm-x86/irqflags.h      Joe Perches               2008-03-23  44  		     :"memory", "cc");
6abcd98f include/asm-x86/irqflags.h      Glauber de Oliveira Costa 2008-01-30  45  }
6abcd98f include/asm-x86/irqflags.h      Glauber de Oliveira Costa 2008-01-30  46  

:::::: The code at line 41 was first introduced by commit
:::::: cf7f7191cf20011e47243b594e433275a6db811b include/asm-x86/irqflags.h: checkpatch cleanups - formatting only

:::::: TO: Joe Perches <joe@...ches.com>
:::::: CC: Ingo Molnar <mingo@...e.hu>

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