Hi NeilBrown,

[auto build test WARNING on next-20170330]
[cannot apply to md/master md/for-next block/for-next linus/master v4.9-rc8 v4.9-rc7 v4.9-rc6 v4.11-rc5]
[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/NeilBrown/Simplify-bio-splitting-and-related-code/20170406-045741
config: x86_64-randconfig-x007-201714 (attached as .config)
compiler: gcc-6 (Debian 6.2.0-3) 6.2.0 20160901
reproduce:
        # save the attached .config to linux build tree
        make ARCH=x86_64 

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 >>):

   drivers/md/raid5.c: In function 'raid5_make_request':
>> drivers/md/raid5.c:5554:6: warning: 'split' may be used uninitialized in this function [-Wmaybe-uninitialized]
      if (!bi)
         ^

vim +/split +5554 drivers/md/raid5.c

828cbe98 Shaohua Li           2015-09-02  5538  		/* ret == -EAGAIN, fallback */
3bddb7f8 Song Liu             2016-11-18  5539  		/*
3bddb7f8 Song Liu             2016-11-18  5540  		 * if r5l_handle_flush_request() didn't clear REQ_PREFLUSH,
3bddb7f8 Song Liu             2016-11-18  5541  		 * we need to flush journal device
3bddb7f8 Song Liu             2016-11-18  5542  		 */
3bddb7f8 Song Liu             2016-11-18  5543  		do_flush = bi->bi_opf & REQ_PREFLUSH;
828cbe98 Shaohua Li           2015-09-02  5544  	}
e5dcdd80 NeilBrown            2005-09-09  5545  
9ffc8f7c Eric Mei             2015-03-18  5546  	/*
9ffc8f7c Eric Mei             2015-03-18  5547  	 * If array is degraded, better not do chunk aligned read because
9ffc8f7c Eric Mei             2015-03-18  5548  	 * later we might have to read it again in order to reconstruct
9ffc8f7c Eric Mei             2015-03-18  5549  	 * data on failed drives.
9ffc8f7c Eric Mei             2015-03-18  5550  	 */
9ffc8f7c Eric Mei             2015-03-18  5551  	if (rw == READ && mddev->degraded == 0 &&
7ef6b12a Ming Lin             2015-05-06  5552  	    mddev->reshape_position == MaxSector) {
7ef6b12a Ming Lin             2015-05-06  5553  		bi = chunk_aligned_read(mddev, bi);
7ef6b12a Ming Lin             2015-05-06 @5554  		if (!bi)
5a7bbad2 Christoph Hellwig    2011-09-12  5555  			return;
7ef6b12a Ming Lin             2015-05-06  5556  	}
52488615 Raz Ben-Jehuda(caro  2006-12-10  5557) 
796a5cf0 Mike Christie        2016-06-05  5558  	if (unlikely(bio_op(bi) == REQ_OP_DISCARD)) {
620125f2 Shaohua Li           2012-10-11  5559  		make_discard_request(mddev, bi);
620125f2 Shaohua Li           2012-10-11  5560  		return;
620125f2 Shaohua Li           2012-10-11  5561  	}
620125f2 Shaohua Li           2012-10-11  5562  

:::::: The code at line 5554 was first introduced by commit
:::::: 7ef6b12a1966f273afb750e19e1e8129bea48fec md/raid5: split bio for chunk_aligned_read

:::::: TO: Ming Lin <ming.l@ssi.samsung.com>
:::::: CC: Jens Axboe <axboe@fb.com>

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