Subject: linux-next: build warning after merge of the btrfs-kdave tree

From: Stephen Rothwell <[email-masked]>
Date: Mon, 26 Nov 2018 11:06:29 +1100

Hi David,

After merging the btrfs-kdave tree, today's linux-next build (powerpc
ppc64_defconfig) produced this warning:

In file included from include/linux/string.h:6,
                 from arch/powerpc/include/asm/paca.h:19,
                 from arch/powerpc/include/asm/current.h:16,
                 from include/linux/sched.h:12,
                 from fs/btrfs/volumes.c:6:
fs/btrfs/volumes.h: In function 'btrfs_op':
include/linux/compiler.h:77:22: warning: this statement may fall through [-Wimplicit-fallthrough=]
 # define unlikely(x) __builtin_expect(!!(x), 0)
                      ^~~~~~~~~~~~~~~~~~~~~~~~~~
include/asm-generic/bug.h:72:2: note: in expansion of macro 'unlikely'
  unlikely(__ret_warn_on);    \
  ^~~~~~~~
fs/btrfs/volumes.h:395:3: note: in expansion of macro 'WARN_ON_ONCE'
   WARN_ON_ONCE(1);
   ^~~~~~~~~~~~
In file included from fs/btrfs/volumes.c:22:
fs/btrfs/volumes.h:396:2: note: here
  case REQ_OP_READ:
  ^~~~

Introduced by commit

  cf8cddd38bab3 ("btrfs: don't abuse REQ_OP_* flags for btrfs_map_block")

exposed by my new use of -Wimplicit-fallthrough

I am not sure why this has only turned up now (as opposed to earlier
today).

-- 
Cheers,
Stephen Rothwell