Re: [PATCH v2 2/2] blk-mq: fix potential uaf for 'queue_hw_ctx'

[kernel test robot <lkp@intel.com>]

Hi Fengnan,

kernel test robot noticed the following build errors:

[auto build test ERROR on 4941a17751c99e17422be743c02c923ad706f888]

url:    https://github.com/intel-lab-lkp/linux/commits/Fengnan-Chang/blk-mq-use-array-manage-hctx-map-instead-of-xarray/20251127-094243
base:   4941a17751c99e17422be743c02c923ad706f888
patch link:    https://lore.kernel.org/r/20251127013908.66118-3-fengnanchang%40gmail.com
patch subject: [PATCH v2 2/2] blk-mq: fix potential uaf for 'queue_hw_ctx'
config: um-allyesconfig (https://download.01.org/0day-ci/archive/20251128/202511280714.MCsRsCmR-lkp@intel.com/config)
compiler: gcc-14 (Debian 14.2.0-19) 14.2.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20251128/202511280714.MCsRsCmR-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202511280714.MCsRsCmR-lkp@intel.com/

All errors (new ones prefixed by >>):

   In file included from drivers/block/rnbd/rnbd-clt.h:16,
                    from drivers/block/rnbd/rnbd-clt.c:19:
   drivers/block/rnbd/rnbd-clt.c: In function 'rnbd_init_mq_hw_queues':
>> include/linux/blk-mq.h:1004:24: error: implicit declaration of function 'queue_hctx' [-Wimplicit-function-declaration]
    1004 |              ({ hctx = queue_hctx((q), i); 1; }); (i)++)
         |                        ^~~~~~~~~~
   drivers/block/rnbd/rnbd-clt.c:1324:9: note: in expansion of macro 'queue_for_each_hw_ctx'
    1324 |         queue_for_each_hw_ctx(dev->queue, hctx, i) {
         |         ^~~~~~~~~~~~~~~~~~~~~
>> include/linux/blk-mq.h:1004:22: error: assignment to 'struct blk_mq_hw_ctx *' from 'int' makes pointer from integer without a cast [-Wint-conversion]
    1004 |              ({ hctx = queue_hctx((q), i); 1; }); (i)++)
         |                      ^
   drivers/block/rnbd/rnbd-clt.c:1324:9: note: in expansion of macro 'queue_for_each_hw_ctx'
    1324 |         queue_for_each_hw_ctx(dev->queue, hctx, i) {
         |         ^~~~~~~~~~~~~~~~~~~~~


vim +/queue_hctx +1004 include/linux/blk-mq.h

  1001	
  1002	#define queue_for_each_hw_ctx(q, hctx, i)				\
  1003		for ((i) = 0; (i) < (q)->nr_hw_queues &&			\
> 1004		     ({ hctx = queue_hctx((q), i); 1; }); (i)++)
  1005	

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