| Message ID | 20160713204342.1221511-1-arnd@arndb.de (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
Hello Arnd, thanks for patch. it looks ok. Acked-by: Abylay Ospan <aospan@netup.ru> 2016-07-13 16:42 GMT-04:00 Arnd Bergmann <arnd@arndb.de>: > 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. > > Signed-off-by: Arnd Bergmann <arnd@arndb.de> > Fixes: (in linux-mm) "dynamic_debug: add jump label support" > --- > drivers/media/dvb-frontends/cxd2841er.c | 10 ++++++++-- > 1 file changed, 8 insertions(+), 2 deletions(-) > > diff --git a/drivers/media/dvb-frontends/cxd2841er.c b/drivers/media/dvb-frontends/cxd2841er.c > index 721fb074da7c..0639ca281a2c 100644 > --- a/drivers/media/dvb-frontends/cxd2841er.c > +++ b/drivers/media/dvb-frontends/cxd2841er.c > @@ -3223,20 +3223,28 @@ 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, > @@ -3244,8 +3252,6 @@ 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; > -- > 2.9.0 >
diff --git a/drivers/media/dvb-frontends/cxd2841er.c b/drivers/media/dvb-frontends/cxd2841er.c index 721fb074da7c..0639ca281a2c 100644 --- a/drivers/media/dvb-frontends/cxd2841er.c +++ b/drivers/media/dvb-frontends/cxd2841er.c @@ -3223,20 +3223,28 @@ 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, @@ -3244,8 +3252,6 @@ 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;
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. Signed-off-by: Arnd Bergmann <arnd@arndb.de> Fixes: (in linux-mm) "dynamic_debug: add jump label support" --- drivers/media/dvb-frontends/cxd2841er.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-)