linux-kernel - Re: [PATCH v3 tip/core/rcu 05/40] rcu: Semicolon inside RCU

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Date:   Tue, 25 Apr 2017 17:13:50 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:     linux-kernel@...r.kernel.org, mingo@...nel.org,
        jiangshanlai@...il.com, dipankar@...ibm.com,
        akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
        josh@...htriplett.org, tglx@...utronix.de, peterz@...radead.org,
        dhowells@...hat.com, edumazet@...gle.com, fweisbec@...il.com,
        oleg@...hat.com, bobby.prani@...il.com
Subject: Re: [PATCH v3 tip/core/rcu 05/40] rcu: Semicolon inside RCU_TRACE()
 for rcu.h

On Wed, 19 Apr 2017 09:58:02 -0700
"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> wrote:

> The current use of "RCU_TRACE(statement);" can cause odd bugs, especially
> where "statement" is a local-variable declaration, as it can leave a
> misplaced ";" in the source code.  This commit therefore converts these
> to "RCU_TRACE(statement;)", which avoids the misplaced ";".
> 
> Reported-by: Josh Triplett <josh@...htriplett.org>
> Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> ---
>  kernel/rcu/rcu.h | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h
> index 0d6ff3e471be..8700a81daf56 100644
> --- a/kernel/rcu/rcu.h
> +++ b/kernel/rcu/rcu.h
> @@ -109,12 +109,12 @@ static inline bool __rcu_reclaim(const char *rn, struct rcu_head *head)
>  
>  	rcu_lock_acquire(&rcu_callback_map);
>  	if (__is_kfree_rcu_offset(offset)) {
> -		RCU_TRACE(trace_rcu_invoke_kfree_callback(rn, head, offset));
> +		RCU_TRACE(trace_rcu_invoke_kfree_callback(rn, head, offset);)

I have to ask. Why is this a RCU_TRACE() anyway? tracepoints use jump
labels, and this is basically a nop here when tracing is off.

-- Steve


>  		kfree((void *)head - offset);
>  		rcu_lock_release(&rcu_callback_map);
>  		return true;
>  	} else {
> -		RCU_TRACE(trace_rcu_invoke_callback(rn, head));
> +		RCU_TRACE(trace_rcu_invoke_callback(rn, head);)
>  		head->func(head);
>  		rcu_lock_release(&rcu_callback_map);
>  		return false;