[dhowells-fs:notifications-pipe-prep 4/10] lib/iov_iter.c:962:34: warning: 'i_head' may be used uninitialized in this function

[dhowells-fs:notifications-pipe-prep 4/10] lib/iov_iter.c:962:34: warning: 'i_head' may be used uninitialized in this function

[kbuild test robot]

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tree:   https://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs.git notifications-pipe-prep
head:   48045df7b3191f476ef0095ec30d6fcbe4411940
commit: 2b988693eb16961453719e63b7a96e83cacd7fd2 [4/10] pipe: Use head and tail pointers for the ring, not cursor and length
config: sparc64-allmodconfig (attached as .config)
compiler: sparc64-linux-gcc (GCC) 7.4.0
reproduce:
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        git checkout 2b988693eb16961453719e63b7a96e83cacd7fd2
        # save the attached .config to linux build tree
        GCC_VERSION=7.4.0 make.cross ARCH=sparc64 

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

   lib/iov_iter.c: In function 'iov_iter_zero':
>> lib/iov_iter.c:962:34: warning: 'i_head' may be used uninitialized in this function [-Wmaybe-uninitialized]
      memzero_page(pipe->bufs[i_head & p_mask].page, off, chunk);
                              ~~~~~~~^~~~~~~~
   lib/iov_iter.c:949:15: note: 'i_head' was declared here
     unsigned int i_head;
                  ^~~~~~

vim +/i_head +962 lib/iov_iter.c

   944	
   945	static size_t pipe_zero(size_t bytes, struct iov_iter *i)
   946	{
   947		struct pipe_inode_info *pipe = i->pipe;
   948		unsigned int p_mask = pipe->ring_size - 1;
   949		unsigned int i_head;
   950		size_t n, off;
   951		int idx;
   952	
   953		if (!sanity(i))
   954			return 0;
   955	
   956		bytes = n = push_pipe(i, bytes, &idx, &off);
   957		if (unlikely(!n))
   958			return 0;
   959	
   960		do {
   961			size_t chunk = min_t(size_t, n, PAGE_SIZE - off);
 > 962			memzero_page(pipe->bufs[i_head & p_mask].page, off, chunk);
   963			i->head = i_head;
   964			i->iov_offset = off + chunk;
   965			n -= chunk;
   966			off = 0;
   967			i_head++;
   968		} while (n);
   969		i->count -= bytes;
   970		return bytes;
   971	}
   972	

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

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