drivers/media/dvb-frontends/cxd2841er.c: avoid misleading gcc warning
authorArnd Bergmann <arnd@arndb.de>
Wed, 3 Aug 2016 20:46:21 +0000 (13:46 -0700)
committerLinus Torvalds <torvalds@linux-foundation.org>
Thu, 4 Aug 2016 12:50:07 +0000 (08:50 -0400)
commitbb9bd878089f365729b9c54012671d289a9a1952
tree45c7d1976d88819928efca772a3ec0abf1ada29c
parent774e0362b20b3e09ed3e63f88bce72a0bdb0a975
drivers/media/dvb-frontends/cxd2841er.c: avoid misleading gcc warning

The addition of jump label support in dynamic_debug caused an unexpected
warning in exactly one file in the kernel:

  drivers/media/dvb-frontends/cxd2841er.c: In function 'cxd2841er_tune_tc':
  include/linux/dynamic_debug.h:134:3: error: 'carrier_offset' may be used uninitialized in this function [-Werror=maybe-uninitialized]
     __dynamic_dev_dbg(&descriptor, dev, fmt, \
     ^~~~~~~~~~~~~~~~~
  drivers/media/dvb-frontends/cxd2841er.c:3177:11: note: 'carrier_offset' was declared here
    int ret, carrier_offset;
             ^~~~~~~~~~~~~~

The problem seems to be that the compiler gets confused by the extra
conditionals in static_branch_unlikely, to the point where it can no
longer keep track of which branches have already been taken, and it
doesn't realize that this variable is now always initialized when it
gets used.

I have done lots of randconfig kernel builds and could not find any
other file with this behavior, so I assume it's a rare enough glitch
that we don't need to change the jump label support but instead just
work around the warning in the driver.

To achieve that, I'm moving the check for the return value into the
switch() statement, which is an obvious transformation, but is enough to
un-confuse the compiler here.  The resulting code is not as nice to
read, but at least we retain the behavior of warning if it gets changed
to actually access an uninitialized carrier offset value in the future.

Link: http://lkml.kernel.org/r/20160713204342.1221511-1-arnd@arndb.de
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Abylay Ospan <aospan@netup.ru>
Cc: Sergey Kozlov <serjk@netup.ru>
Cc: Mauro Carvalho Chehab <mchehab@kernel.org>
Cc: Jason Baron <jbaron@akamai.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
drivers/media/dvb-frontends/cxd2841er.c