On Sat, Jan 18, 2020 at 09:14:25PM -0500, Joel Fernandes wrote:
> On Sat, Jan 18, 2020 at 10:24:18PM +0530, Amol Grover wrote:
> > Passing a complex lockdep condition to __list_check_rcu results
> > in false positive lockdep splat due to incorrect expression
> > evaluation.
> >
> > For example, a lockdep check condition `cond1 || cond2` is
> > evaluated as `!cond1 || cond2 && !rcu_read_lock_any_held()`
> > which, according to operator precedence, evaluates to
> > `!cond1 || (cond2 && !rcu_read_lock_any_held())`.
> > This would result in a lockdep splat when cond1 is false
> > and cond2 is true which is logically incorrect.
> >
> > Signed-off-by: Amol Grover <frextrite@xxxxxxxxx>
>
> Good catch!
>
> Acked-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx>
Queued for v5.7, thank you both!
Thanx, Paul
> thanks,
>
> - Joel
>
>
> > ---
> > include/linux/rculist.h | 4 ++--
> > 1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/include/linux/rculist.h b/include/linux/rculist.h
> > index 4158b7212936..dce491f0b354 100644
> > --- a/include/linux/rculist.h
> > +++ b/include/linux/rculist.h
> > @@ -50,9 +50,9 @@ static inline void INIT_LIST_HEAD_RCU(struct list_head *list)
> > #define __list_check_rcu(dummy, cond, extra...) \
> > ({ \
> > check_arg_count_one(extra); \
> > - RCU_LOCKDEP_WARN(!cond && !rcu_read_lock_any_held(), \
> > + RCU_LOCKDEP_WARN(!(cond) && !rcu_read_lock_any_held(), \
> > "RCU-list traversed in non-reader section!"); \
> > - })
> > + })
> > #else
> > #define __list_check_rcu(dummy, cond, extra...) \
> > ({ check_arg_count_one(extra); })
> > --
> > 2.24.1
> >
