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From: Joel Fernandes <joel@joelfernandes.org>
To: Amol Grover <frextrite@gmail.com>
Cc: "Paul E. McKenney" <paulmck@kernel.org>,
	Lai Jiangshan <jiangshanlai@gmail.com>,
	Josh Triplett <josh@joshtriplett.org>,
	Steven Rostedt <rostedt@goodmis.org>,
	linux-kernel@vger.kernel.org, rcu@vger.kernel.org,
	Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
	linux-kernel-mentees@lists.linuxfoundation.org
Subject: Re: [Linux-kernel-mentees] [PATCH] rculist: Add brackets around cond argument in __list_check_rcu macro
Date: Sat, 18 Jan 2020 21:14:25 -0500	[thread overview]
Message-ID: <20200119021425.GH244899@google.com> (raw)
In-Reply-To: <20200118165417.12325-1-frextrite@gmail.com>

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>

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
> 
_______________________________________________
Linux-kernel-mentees mailing list
Linux-kernel-mentees@lists.linuxfoundation.org
https://lists.linuxfoundation.org/mailman/listinfo/linux-kernel-mentees

WARNING: multiple messages have this Message-ID (diff)
From: Joel Fernandes <joel@joelfernandes.org>
To: Amol Grover <frextrite@gmail.com>
Cc: "Paul E. McKenney" <paulmck@kernel.org>,
	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: Sat, 18 Jan 2020 21:14:25 -0500	[thread overview]
Message-ID: <20200119021425.GH244899@google.com> (raw)
In-Reply-To: <20200118165417.12325-1-frextrite@gmail.com>

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>

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
> 

  reply	other threads:[~2020-01-19  2:14 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-18 16:54 [Linux-kernel-mentees] [PATCH] rculist: Add brackets around cond argument in __list_check_rcu macro Amol Grover
2020-01-18 16:54 ` Amol Grover
2020-01-19  2:14 ` Joel Fernandes [this message]
2020-01-19  2:14   ` Joel Fernandes
2020-01-21  0:00   ` [Linux-kernel-mentees] " Paul E. McKenney
2020-01-21  0:00     ` Paul E. McKenney

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