From: "Paul E. McKenney" <paulmck@kernel.org>
To: Joel Fernandes <joel@joelfernandes.org>
Cc: Amol Grover <frextrite@gmail.com>,
Josh Triplett <josh@joshtriplett.org>,
Steven Rostedt <rostedt@goodmis.org>,
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
Lai Jiangshan <jiangshanlai@gmail.com>,
rcu@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-kernel-mentees@lists.linuxfoundation.org,
Madhuparna Bhowmik <madhuparnabhowmik04@gmail.com>
Subject: Re: [PATCH] rculist: Add brackets around cond argument in __list_check_rcu macro
Date: Mon, 20 Jan 2020 16:00:58 -0800 [thread overview]
Message-ID: <20200121000058.GI2935@paulmck-ThinkPad-P72> (raw)
In-Reply-To: <20200119021425.GH244899@google.com>
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@gmail.com>
>
> Good catch!
>
> Acked-by: Joel Fernandes (Google) <joel@joelfernandes.org>
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
> >
prev parent reply other threads:[~2020-01-21 0:01 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-18 16:54 [PATCH] rculist: Add brackets around cond argument in __list_check_rcu macro Amol Grover
2020-01-19 2:14 ` Joel Fernandes
2020-01-21 0:00 ` Paul E. McKenney [this message]
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