[smatch stuff] md/raid5: potential null deref in debug code

[Dan Carpenter <error27@gmail.com>]

Hi Neil,

In d1b053e4de0ac33 "md/raid5: Protect some more code with
->device_lock." we moved some debug code around and it upsets my
static checker.  Could you take a look?

drivers/md/raid5.c +2183 add_stripe_bio(47)
	error: potential null derefence 'bi'.

  2168          if (forwrite) {
  2169                  /* check if page is covered */
  2170                  sector_t sector = sh->dev[dd_idx].sector;
  2171                  for (bi=sh->dev[dd_idx].towrite;
  2172                       sector < sh->dev[dd_idx].sector + STRIPE_SECTORS &&
  2173                               bi && bi->bi_sector <= sector;
                                     ^^
	It looks like "bi" can be NULL at the end of this for loop.


  2174                       bi = r5_next_bio(bi, sh->dev[dd_idx].sector)) {
  2175                          if (bi->bi_sector + (bi->bi_size>>9) >= sector)
  2176                                  sector = bi->bi_sector + (bi->bi_size>>9);
  2177                  }
  2178                  if (sector >= sh->dev[dd_idx].sector + STRIPE_SECTORS)
  2179                          set_bit(R5_OVERWRITE, &sh->dev[dd_idx].flags);
  2180          }
  2181          spin_unlock_irq(&conf->device_lock);
  2182  
  2183          pr_debug("added bi b#%llu to stripe s#%llu, disk %d.\n",
  2184                  (unsigned long long)bi->bi_sector,
                                            ^^^^^^^^^^^^^
	We dereference it here.

  2185                  (unsigned long long)sh->sector, dd_idx);

regards,
dan carpenter