linux-kernel - Re: [PATCH -v2] ipvs: Remove unused variable ret from sync_thread

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Date:	Wed, 13 Nov 2013 10:00:39 +0200 (EET)
From:	Julian Anastasov <ja@....bg>
To:	Geert Uytterhoeven <geert@...ux-m68k.org>
cc:	Peter Zijlstra <peterz@...radead.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Ingo Molnar <mingo@...nel.org>, netdev@...r.kernel.org,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Simon Horman <horms@...ge.net.au>,
	Fabio Estevam <festevam@...il.com>
Subject: Re: [PATCH -v2] ipvs: Remove unused variable ret from
 sync_thread_master()


	Hello,

On Tue, 12 Nov 2013, Geert Uytterhoeven wrote:

> net/netfilter/ipvs/ip_vs_sync.c: In function 'sync_thread_master':
> net/netfilter/ipvs/ip_vs_sync.c:1640:8: warning: unused variable 'ret' [-Wunused-variable]
> 
> Commit 35a2af94c7ce7130ca292c68b1d27fcfdb648f6b ("sched/wait: Make the
> __wait_event*() interface more friendly") changed how the interruption
> state is returned. However, sync_thread_master() ignores this state,
> now causing a compile warning.
> 
> According to Julian Anastasov <ja@....bg>, this behavior is OK:
> 
>     "Yes, your patch looks ok to me. In the past we used ssleep() but IPVS
>      users were confused why IPVS threads increase the load average. So, we
>      switched to _interruptible calls and later the socket polling was
>      added."
> 
> Document this, as requested by Peter Zijlstra, to avoid precious developers
> disappearing in this pitfall in the future.
> 
> Signed-off-by: Geert Uytterhoeven <geert@...ux-m68k.org>
> ---
> v2: Document that sync_thread_master() ignores the interruption state,
> 
>  net/netfilter/ipvs/ip_vs_sync.c |    5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/net/netfilter/ipvs/ip_vs_sync.c b/net/netfilter/ipvs/ip_vs_sync.c
> index f63c2388f38d..db801263ee9f 100644
> --- a/net/netfilter/ipvs/ip_vs_sync.c
> +++ b/net/netfilter/ipvs/ip_vs_sync.c
> @@ -1637,7 +1637,10 @@ static int sync_thread_master(void *data)
>  			continue;
>  		}
>  		while (ip_vs_send_sync_msg(tinfo->sock, sb->mesg) < 0) {
> -			int ret = __wait_event_interruptible(*sk_sleep(sk),
> +			/* (Ab)use interruptible sleep to avoid increasing
> +			 * the load avg.
> +			 */
> +			__wait_event_interruptible(*sk_sleep(sk),
>  						   sock_writeable(sk) ||
>  						   kthread_should_stop());
>  			if (unlikely(kthread_should_stop()))

	Fabio Estevam posted similar change too early but
we are better with such comment.

Acked-by: Julian Anastasov <ja@....bg>

	Also, the TASK_UNINTERRUPTIBLE | TASK_IDLE idea looks good
to me. If such change is planned may be the above patch
better not to go via the ipvs-next tree to avoid conflicts?
As we don't have any changes in this area let us know if
someone takes the above patch for another tree.

Regards

--
Julian Anastasov <ja@....bg>
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