[linux-stable-rc:linux-4.14.y 9470/9484] fs/proc/task_mmu.c:761:7: warning: 'last_vma' may be used uninitialized in this function

[linux-stable-rc:linux-4.14.y 9470/9484] fs/proc/task_mmu.c:761:7: warning: 'last_vma' may be used uninitialized in this function

[kbuild test robot]

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tree:   https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable-rc.git linux-4.14.y
head:   fea4e6b46436daf1982a367f638e3f5e0ae1bd3f
commit: 7c0e08d8ed3b8b6cf287007968d130f737256438 [9470/9484] mm: proc: smaps_rollup: fix pss_locked calculation
config: i386-randconfig-s1-02172359 (attached as .config)
compiler: gcc-6 (Debian 6.5.0-2) 6.5.0 20181026
reproduce:
        git checkout 7c0e08d8ed3b8b6cf287007968d130f737256438
        # save the attached .config to linux build tree
        make ARCH=i386 

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 >>):

   fs/proc/task_mmu.c: In function 'show_smap.isra.38':
>> fs/proc/task_mmu.c:761:7: warning: 'last_vma' may be used uninitialized in this function [-Wmaybe-uninitialized]
     bool last_vma;
          ^~~~~~~~

vim +/last_vma +761 fs/proc/task_mmu.c

c1192f842 Dave Hansen        2016-02-12  745  
b76437579 Siddhesh Poyarekar 2012-03-21  746  static int show_smap(struct seq_file *m, void *v, int is_pid)
e070ad49f Mauricio Lin       2005-09-03  747  {
493b0e9d9 Daniel Colascione  2017-09-06  748  	struct proc_maps_private *priv = m->private;
e070ad49f Mauricio Lin       2005-09-03  749  	struct vm_area_struct *vma = v;
493b0e9d9 Daniel Colascione  2017-09-06  750  	struct mem_size_stats mss_stack;
493b0e9d9 Daniel Colascione  2017-09-06  751  	struct mem_size_stats *mss;
2165009bd Dave Hansen        2008-06-12  752  	struct mm_walk smaps_walk = {
2165009bd Dave Hansen        2008-06-12  753  		.pmd_entry = smaps_pte_range,
25ee01a2f Naoya Horiguchi    2015-11-05  754  #ifdef CONFIG_HUGETLB_PAGE
25ee01a2f Naoya Horiguchi    2015-11-05  755  		.hugetlb_entry = smaps_hugetlb_range,
25ee01a2f Naoya Horiguchi    2015-11-05  756  #endif
2165009bd Dave Hansen        2008-06-12  757  		.mm = vma->vm_mm,
2165009bd Dave Hansen        2008-06-12  758  	};
493b0e9d9 Daniel Colascione  2017-09-06  759  	int ret = 0;
493b0e9d9 Daniel Colascione  2017-09-06  760  	bool rollup_mode;
493b0e9d9 Daniel Colascione  2017-09-06 @761  	bool last_vma;
493b0e9d9 Daniel Colascione  2017-09-06  762  
493b0e9d9 Daniel Colascione  2017-09-06  763  	if (priv->rollup) {
493b0e9d9 Daniel Colascione  2017-09-06  764  		rollup_mode = true;
493b0e9d9 Daniel Colascione  2017-09-06  765  		mss = priv->rollup;
493b0e9d9 Daniel Colascione  2017-09-06  766  		if (mss->first) {
493b0e9d9 Daniel Colascione  2017-09-06  767  			mss->first_vma_start = vma->vm_start;
493b0e9d9 Daniel Colascione  2017-09-06  768  			mss->first = false;
493b0e9d9 Daniel Colascione  2017-09-06  769  		}
493b0e9d9 Daniel Colascione  2017-09-06  770  		last_vma = !m_next_vma(priv, vma);
493b0e9d9 Daniel Colascione  2017-09-06  771  	} else {
493b0e9d9 Daniel Colascione  2017-09-06  772  		rollup_mode = false;
493b0e9d9 Daniel Colascione  2017-09-06  773  		memset(&mss_stack, 0, sizeof(mss_stack));
493b0e9d9 Daniel Colascione  2017-09-06  774  		mss = &mss_stack;
493b0e9d9 Daniel Colascione  2017-09-06  775  	}
e070ad49f Mauricio Lin       2005-09-03  776  
493b0e9d9 Daniel Colascione  2017-09-06  777  	smaps_walk.private = mss;
c261e7d94 Vlastimil Babka    2016-01-14  778  

:::::: The code at line 761 was first introduced by commit
:::::: 493b0e9d945fa9dfe96be93ae41b4ca4b6fdb317 mm: add /proc/pid/smaps_rollup

:::::: TO: Daniel Colascione <dancol@google.com>
:::::: CC: Linus Torvalds <torvalds@linux-foundation.org>

---
0-DAY kernel test infrastructure                Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all                   Intel Corporation

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Re: [linux-stable-rc:linux-4.14.y 9470/9484] fs/proc/task_mmu.c:761:7: warning: 'last_vma' may be used uninitialized in this function

[Vlastimil Babka]

On 2/18/19 9:01 PM, kbuild test robot wrote:
> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable-rc.git linux-4.14.y
> head:   fea4e6b46436daf1982a367f638e3f5e0ae1bd3f
> commit: 7c0e08d8ed3b8b6cf287007968d130f737256438 [9470/9484] mm: proc: smaps_rollup: fix pss_locked calculation
> config: i386-randconfig-s1-02172359 (attached as .config)
> compiler: gcc-6 (Debian 6.5.0-2) 6.5.0 20181026
> reproduce:
>         git checkout 7c0e08d8ed3b8b6cf287007968d130f737256438
>         # save the attached .config to linux build tree
>         make ARCH=i386 
> 
> 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 >>):
> 
>    fs/proc/task_mmu.c: In function 'show_smap.isra.38':
>>> fs/proc/task_mmu.c:761:7: warning: 'last_vma' may be used uninitialized in this function [-Wmaybe-uninitialized]
>      bool last_vma;
>           ^~~~~~~~

AFAICS false positive, and the commit in question doesn't touch that part.