Re: [PATCH] power: opp: Fix rcu_dereference_check() without protection!

[Santosh Shilimkar]

On 6/14/2011 9:08 PM, Menon, Nishanth wrote:
> On Tue, Jun 14, 2011 at 08:03, Santosh Shilimkar
> <santosh.shilimkar@xxxxxx>  wrote:
> > With RCU debug options enabled, below warning is observed.
> >
> > ===================================================
> > [ INFO: suspicious rcu_dereference_check() usage. ]
> > ---------------------------------------------------
> > drivers/base/power/opp.c:151 invoked rcu_dereference_check() without protection!
> >
> > other info that might help us debug this:
> >
> > rcu_scheduler_active = 1, debug_locks = 1
> > no locks held by swapper/1.
> > ...
> >
> > ---------------------------------------------------
> >
> > Fix the same by protecting it with rcu_read lock.
> >
> > Signed-off-by: Santosh Shilimkar<santosh.shilimkar@xxxxxx>
> > Cc: Rafael J. Wysocki<rjw@xxxxxxx>
> > Cc: Nishanth Menon<nm@xxxxxx>
> > Cc: Kevin Hilman<khilman@xxxxxxxxxxxxxxxxxxx>
> > ---
> >   drivers/base/power/opp.c |    2 ++
> >   1 files changed, 2 insertions(+), 0 deletions(-)
> >
> > diff --git a/drivers/base/power/opp.c b/drivers/base/power/opp.c
> > index 56a6899..cbed5e1 100644
> > --- a/drivers/base/power/opp.c
> > +++ b/drivers/base/power/opp.c
> > @@ -148,7 +148,9 @@ unsigned long opp_get_voltage(struct opp *opp)
> >         struct opp *tmp_opp;
> >         unsigned long v = 0;
> >
> > +       rcu_read_lock();
> >         tmp_opp = rcu_dereference(opp);
> > +       rcu_read_unlock();
> >         if (unlikely(IS_ERR_OR_NULL(tmp_opp)) || !tmp_opp->available)
> >                 pr_err("%s: Invalid parameters\n", __func__);
> >         else
> NAK. please read the Documentation/power/opp.txt
> the usage is as follows:
> rcu_read_lock();
> opp = opp_find_freq_ceil();
> voltage = opp_get_voltage(opp);
> rcu_read_unlock();
>
> the reason for this is that the opp pointer is not safe if we lock
> just the dereferencing.
Fair enough. if the whole fn is under the lock then it's not
necessary.

Regards
Santosh
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/