On Thu, Dec 21, 2017 at 12:35:21AM +0800, kbuild test robot wrote:

Thank you for the patch! Perhaps something to improve:

[auto build test WARNING on linus/master]
[also build test WARNING on v4.15-rc4 next-20171220]
[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/Tomasz-Majchrzak/raid5-ppl-PPL-support-for-disks-with-write-back-cache-enabled/20171220-181528
reproduce:
        # apt-get install sparse
        make ARCH=x86_64 allmodconfig
        make C=1 CF=-D__CHECK_ENDIAN__


   633	
   634			rcu_read_lock();
 > 635			rdev = rcu_dereference(conf->disks[i].rdev);
   636			if (rdev && test_bit(Faulty, &rdev->flags))
   637				rdev = NULL;
   638			rcu_read_unlock();

The warning from sparse is:

drivers/md/raid5-ppl.c:635:24: error: incompatible types in comparison expression (different address spaces)

There is the same warning for 20 other places in md raid5 code, everywhere
where rcu_dereference is used so I understand the probles is either in sparse
or in function implementation.

Tomek