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>

1 files changed, 8 insertions, 2 deletions

diff --git a/drivers/media/dvb-frontends/cxd2841er.c b/drivers/media/dvb-frontends/cxd2841er.c
index 09c39346167f..ffe88bc6b813 100644
--- a/drivers/media/dvb-frontends/cxd2841er.c
+++ b/drivers/media/dvb-frontends/cxd2841er.c
@@ -3378,20 +3378,28 @@ static int cxd2841er_tune_tc(struct dvb_frontend *fe,
 				ret = cxd2841er_get_carrier_offset_i(
 						priv, p->bandwidth_hz,
 						&carrier_offset);
+				if (ret)
+					return ret;
 				break;
 			case SYS_DVBT:
 				ret = cxd2841er_get_carrier_offset_t(
 					priv, p->bandwidth_hz,
 					&carrier_offset);
+				if (ret)
+					return ret;
 				break;
 			case SYS_DVBT2:
 				ret = cxd2841er_get_carrier_offset_t2(
 					priv, p->bandwidth_hz,
 					&carrier_offset);
+				if (ret)
+					return ret;
 				break;
 			case SYS_DVBC_ANNEX_A:
 				ret = cxd2841er_get_carrier_offset_c(
 					priv, &carrier_offset);
+				if (ret)
+					return ret;
 				break;
 			default:
 				dev_dbg(&priv->i2c->dev,
@@ -3399,8 +3407,6 @@ static int cxd2841er_tune_tc(struct dvb_frontend *fe,
 					__func__, priv->system);
 				return -EINVAL;
 			}
-			if (ret)
-				return ret;
 			dev_dbg(&priv->i2c->dev, "%s(): carrier offset %d\n",
 				__func__, carrier_offset);
 			p->frequency += carrier_offset;