Re: [PATCH v2 1/2] livepatch: introduce shadow variable API

[Joe Lawrence <joe.lawrence@redhat.com>]

On Fri, Jun 30, 2017 at 09:49:46PM +0800, kbuild test robot wrote:
> Date: Fri, 30 Jun 2017 21:49:46 +0800
> From: kbuild test robot <lkp@intel.com>
> To: Joe Lawrence <joe.lawrence@redhat.com>
> Cc: kbuild-all@01.org, live-patching@vger.kernel.org,
>  linux-kernel@vger.kernel.org, Josh Poimboeuf <jpoimboe@redhat.com>,
>  Jessica Yu <jeyu@redhat.com>, Jiri Kosina <jikos@kernel.org>, Miroslav
>  Benes <mbenes@suse.cz>, Petr Mladek <pmladek@suse.com>
> Subject: Re: [PATCH v2 1/2] livepatch: introduce shadow variable API
> User-Agent: Mutt/1.5.23 (2014-03-12)
> 
> Hi Joe,
> 
> [auto build test WARNING on jikos-livepatching/for-next]
> [also build test WARNING on v4.12-rc7 next-20170630]
> [if your patch is applied to the wrong git tree, please drop us a note to help improve the system]
> 
> url:    https://github.com/0day-ci/linux/commits/Joe-Lawrence/livepatch-introduce-shadow-variable-API/20170630-061942
> base:   https://git.kernel.org/pub/scm/linux/kernel/git/jikos/livepatching.git for-next
> config: s390-performance_defconfig (attached as .config)
> compiler: s390x-linux-gnu-gcc (Debian 6.1.1-9) 6.1.1 20160705
> reproduce:
>         wget https://raw.githubusercontent.com/01org/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
>         chmod +x ~/bin/make.cross
>         # save the attached .config to linux build tree
>         make.cross ARCH=s390 
> 
> 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:15:0,
>                     from arch/s390/include/asm/processor.h:35,
>                     from arch/s390/include/asm/thread_info.h:24,
>                     from include/linux/thread_info.h:37,
>                     from arch/s390/include/asm/preempt.h:5,
>                     from include/linux/preempt.h:80,
>                     from include/linux/spinlock.h:50,
>                     from include/linux/rcupdate.h:38,
>                     from include/linux/rculist.h:10,
>                     from include/linux/hashtable.h:13,
>                     from kernel/livepatch/shadow.c:49:
>    kernel/livepatch/shadow.c: In function '_klp_shadow_attach':
> >> arch/s390/include/asm/irqflags.h:63:12: warning: 'flags' may be used uninitialized in this function [-Wmaybe-uninitialized]
>      if (flags & ARCH_IRQ_ENABLED)
>                ^
>    kernel/livepatch/shadow.c:135:16: note: 'flags' was declared here
>      unsigned long flags;
>                    ^~~~~
> --
>    In file included from include/linux/irqflags.h:15:0,
>                     from arch/s390/include/asm/processor.h:35,
>                     from arch/s390/include/asm/thread_info.h:24,
>                     from include/linux/thread_info.h:37,
>                     from arch/s390/include/asm/preempt.h:5,
>                     from include/linux/preempt.h:80,
>                     from include/linux/spinlock.h:50,
>                     from include/linux/rcupdate.h:38,
>                     from include/linux/rculist.h:10,
>                     from include/linux/hashtable.h:13,
>                     from kernel//livepatch/shadow.c:49:
>    kernel//livepatch/shadow.c: In function '_klp_shadow_attach':
> >> arch/s390/include/asm/irqflags.h:63:12: warning: 'flags' may be used uninitialized in this function [-Wmaybe-uninitialized]
>      if (flags & ARCH_IRQ_ENABLED)
>                ^
>    kernel//livepatch/shadow.c:135:16: note: 'flags' was declared here
>      unsigned long flags;
>                    ^~~~~
> 
> vim +/flags +63 arch/s390/include/asm/irqflags.h
> 
> 94c12cc7d include/asm-s390/irqflags.h      Martin Schwidefsky    2006-09-28  47  }
> 94c12cc7d include/asm-s390/irqflags.h      Martin Schwidefsky    2006-09-28  48  
> f433c4aec arch/s390/include/asm/irqflags.h Steven Rostedt        2011-07-24  49  static inline notrace void arch_local_irq_disable(void)
> df9ee2927 arch/s390/include/asm/irqflags.h David Howells         2010-10-07  50  {
> df9ee2927 arch/s390/include/asm/irqflags.h David Howells         2010-10-07  51  	arch_local_irq_save();
> df9ee2927 arch/s390/include/asm/irqflags.h David Howells         2010-10-07  52  }
> 1f194a4c3 include/asm-s390/irqflags.h      Heiko Carstens        2006-07-03  53  
> f433c4aec arch/s390/include/asm/irqflags.h Steven Rostedt        2011-07-24  54  static inline notrace void arch_local_irq_enable(void)
> 94c12cc7d include/asm-s390/irqflags.h      Martin Schwidefsky    2006-09-28  55  {
> df9ee2927 arch/s390/include/asm/irqflags.h David Howells         2010-10-07  56  	__arch_local_irq_stosm(0x03);
> 94c12cc7d include/asm-s390/irqflags.h      Martin Schwidefsky    2006-09-28  57  }
> 1f194a4c3 include/asm-s390/irqflags.h      Heiko Carstens        2006-07-03  58  
> 204ee2c56 arch/s390/include/asm/irqflags.h Christian Borntraeger 2016-01-11  59  /* This only restores external and I/O interrupt state */
> f433c4aec arch/s390/include/asm/irqflags.h Steven Rostedt        2011-07-24  60  static inline notrace void arch_local_irq_restore(unsigned long flags)
> df9ee2927 arch/s390/include/asm/irqflags.h David Howells         2010-10-07  61  {
> 204ee2c56 arch/s390/include/asm/irqflags.h Christian Borntraeger 2016-01-11  62  	/* only disabled->disabled and disabled->enabled is valid */
> 204ee2c56 arch/s390/include/asm/irqflags.h Christian Borntraeger 2016-01-11 @63  	if (flags & ARCH_IRQ_ENABLED)
> 204ee2c56 arch/s390/include/asm/irqflags.h Christian Borntraeger 2016-01-11  64  		arch_local_irq_enable();
> df9ee2927 arch/s390/include/asm/irqflags.h David Howells         2010-10-07  65  }
> df9ee2927 arch/s390/include/asm/irqflags.h David Howells         2010-10-07  66  
> f433c4aec arch/s390/include/asm/irqflags.h Steven Rostedt        2011-07-24  67  static inline notrace bool arch_irqs_disabled_flags(unsigned long flags)
> 1f194a4c3 include/asm-s390/irqflags.h      Heiko Carstens        2006-07-03  68  {
> 204ee2c56 arch/s390/include/asm/irqflags.h Christian Borntraeger 2016-01-11  69  	return !(flags & ARCH_IRQ_ENABLED);
> 1f194a4c3 include/asm-s390/irqflags.h      Heiko Carstens        2006-07-03  70  }
> 1f194a4c3 include/asm-s390/irqflags.h      Heiko Carstens        2006-07-03  71  
> 
> :::::: The code at line 63 was first introduced by commit
> :::::: 204ee2c5643199a25181ec04ea645d00709c2a5a s390/irqflags: optimize irq restore
> 
> :::::: TO: Christian Borntraeger <borntraeger@de.ibm.com>
> :::::: CC: Martin Schwidefsky <schwidefsky@de.ibm.com>
> 
> ---
> 0-DAY kernel test infrastructure                Open Source Technology Center
> https://lists.01.org/pipermail/kbuild-all                   Intel Corporation

Presumably the 0-day built bot doesn't like this construct:

	static void *_klp_shadow_attach(void *obj, unsigned long num, void *new_data,
					size_t new_size, gfp_t gfp_flags,
					bool lock)
	{
		unsigned long flags;
		...
		if (lock)
			spin_lock_irqsave(&klp_shadow_lock, flags);
		hash_add_rcu(klp_shadow_hash, &shadow->node, (unsigned long)obj);
		if (lock)
			spin_unlock_irqrestore(&klp_shadow_lock, flags);

Perhaps explicitly initializing flags to 0, or combining the conditional
will appease it?

-- Joe