linux-kernel - Re: [PATCH V2] rcu: change return type to bool

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Date:	Wed, 27 May 2015 14:19:31 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Nicholas Mc Guire <hofrat@...dl.org>
Cc:	Lai Jiangshan <laijs@...fujitsu.com>,
	Josh Triplett <josh@...htriplett.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Joe Perches <joe@...ches.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH V2] rcu: change return type to bool

On Wed, May 27, 2015 at 08:56:25AM +0200, Nicholas Mc Guire wrote:
> Type-checking coccinelle spatches are being used to locate type mismatches
> between function signatures and return values in this case this produced:
> ./kernel/rcu/srcu.c:271 WARNING: return of wrong type
>         int != unsigned long,
> 
> srcu_readers_active() returns an int that is the sum of per_cpu unsigned
> long but the only user is cleanup_srcu_struct() which is using it as a
> boolean (condition) to see if there is any readers rather than actually
> using the approximate number of readers. The theoretically possible
> unsigned long overflow case does not need to be handled explicitly - if
> we had 4G++ readers then something else went wrong a long time ago.
> 
> proposal: change the return type to boolean. The function name is left
>           unchanged as it fits the naming expectation for a boolean.
> 
> patch was compile tested for x86_64_defconfig (implies CONFIG_SRCU=y)
> 
> patch is against 4.1-rc5 (localversion-next is -next-20150525)
> 
> Signed-off-by: Nicholas Mc Guire <hofrat@...dl.org>

OK, I have queued this for testing.  If Lai Jiangshan is OK with it,
I am OK with it.

							Thanx, Paul

> ---
> 
> V2: dropped the unnecessary !! conversion to boolean. for the details
>     see Joe Perches <joe@...ches.com> clarification at
>     http://lkml.org/lkml/2015/5/24/47
> 
>  kernel/rcu/srcu.c |    5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/rcu/srcu.c b/kernel/rcu/srcu.c
> index fb33d35..de35087 100644
> --- a/kernel/rcu/srcu.c
> +++ b/kernel/rcu/srcu.c
> @@ -252,14 +252,15 @@ static bool srcu_readers_active_idx_check(struct srcu_struct *sp, int idx)
>  }
> 
>  /**
> - * srcu_readers_active - returns approximate number of readers.
> + * srcu_readers_active - returns true if there are readers. and false
> + *                       otherwise
>   * @sp: which srcu_struct to count active readers (holding srcu_read_lock).
>   *
>   * Note that this is not an atomic primitive, and can therefore suffer
>   * severe errors when invoked on an active srcu_struct.  That said, it
>   * can be useful as an error check at cleanup time.
>   */
> -static int srcu_readers_active(struct srcu_struct *sp)
> +static bool srcu_readers_active(struct srcu_struct *sp)
>  {
>  	int cpu;
>  	unsigned long sum = 0;
> -- 
> 1.7.10.4
> 

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