linux-kernel - Re: [PATCH] acct: eliminate compile warning

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Message-Id: <20140826162501.7c05fa936e79c07927681bad@linux-foundation.org>
Date:	Tue, 26 Aug 2014 16:25:01 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Ying Xue <ying.xue@...driver.com>
Cc:	<linux-kernel@...r.kernel.org>, <viro@...iv.linux.org.uk>,
	<jack@...e.cz>
Subject: Re: [PATCH] acct: eliminate compile warning

On Thu, 21 Aug 2014 09:58:46 +0800 Ying Xue <ying.xue@...driver.com> wrote:

> If ACCT_VERSION is not defined to 3, below warning appears:
>   CC      kernel/acct.o
>   kernel/acct.c: In function ___do_acct_process___:
>   kernel/acct.c:475:24: warning: unused variable ___ns___ [-Wunused-variable]
> 
> Signed-off-by: Ying Xue <ying.xue@...driver.com>
> ---
>  kernel/acct.c |    6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/acct.c b/kernel/acct.c
> index b4c667d..bb52701 100644
> --- a/kernel/acct.c
> +++ b/kernel/acct.c
> @@ -472,7 +472,6 @@ static void do_acct_process(struct bsd_acct_struct *acct)
>  	acct_t ac;
>  	unsigned long flim;
>  	const struct cred *orig_cred;
> -	struct pid_namespace *ns = acct->ns;
>  	struct file *file = acct->file;
>  
>  	/*
> @@ -500,9 +499,10 @@ static void do_acct_process(struct bsd_acct_struct *acct)
>  	ac.ac_gid16 = ac.ac_gid;
>  #endif
>  #if ACCT_VERSION == 3
> -	ac.ac_pid = task_tgid_nr_ns(current, ns);
> +	ac.ac_pid = task_tgid_nr_ns(current, acct->ns);
>  	rcu_read_lock();
> -	ac.ac_ppid = task_tgid_nr_ns(rcu_dereference(current->real_parent), ns);
> +	ac.ac_ppid = task_tgid_nr_ns(rcu_dereference(current->real_parent),
> +				     acct->ns);
>  	rcu_read_unlock();
>  #endif

With my gcc this change increases .text from 5429 to 5437 bytes.  If we
do it this way:

--- a/kernel/acct.c~acct-eliminate-compile-warning-fix
+++ a/kernel/acct.c
@@ -499,11 +499,15 @@ static void do_acct_process(struct bsd_a
 	ac.ac_gid16 = ac.ac_gid;
 #endif
 #if ACCT_VERSION == 3
-	ac.ac_pid = task_tgid_nr_ns(current, acct->ns);
-	rcu_read_lock();
-	ac.ac_ppid = task_tgid_nr_ns(rcu_dereference(current->real_parent),
-				     acct->ns);
-	rcu_read_unlock();
+	{
+		struct pid_namespace *ns = acct->ns;
+
+		ac.ac_pid = task_tgid_nr_ns(current, ns);
+		rcu_read_lock();
+		ac.ac_ppid = task_tgid_nr_ns(rcu_dereference(current->real_parent),
+					     ns);
+		rcu_read_unlock();
+	}
 #endif
 	/*
 	 * Get freeze protection. If the fs is frozen, just skip the write

it actually shrinks to 5415 bytes.  Weird.


We could actually do

	if (ACCT_VERSION == 3)
		...

in lots of places in acct.c.  The code would be less ugly and
compilation coverage testing would improve.
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