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Subject: Re: [PATCH] slow_work_thread() should do the exclusive wait
From: Trond Myklebust <Trond.Myklebust@netapp.com>
To: Oleg Nesterov <oleg@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
       David Howells <dhowells@redhat.com>, Serge Hallyn <serue@us.ibm.com>,
       Steve Dickson <steved@redhat.com>, Al Viro <viro@zeniv.linux.org.uk>,
       Daire Byrne <Daire.Byrne@framestore.com>, linux-kernel@vger.kernel.org
In-Reply-To: <20090413181733.GA10424@redhat.com>
References: <20090413181733.GA10424@redhat.com>
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Organization: NetApp
Date: Mon, 13 Apr 2009 15:03:49 -0400
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On Mon, 2009-04-13 at 20:17 +0200, Oleg Nesterov wrote:
> slow_work_thread() sleeps on slow_work_thread_wq without WQ_FLAG_EXCLUSIVE,
> this means that slow_work_enqueue()->__wake_up(nr_exclusive => 1) wakes up
> all kslowd threads. Afaics this is not what we want, change slow_work_thread()
> to use prepare_to_wait_exclusive().
> 
> Signed-off-by: Oleg Nesterov <oleg@redhat.com>
> 
> --- 6.30/kernel/slow-work.c~1_SW_EXCLUSIVE	2009-04-06 00:03:42.000000000 +0200
> +++ 6.30/kernel/slow-work.c	2009-04-13 19:40:20.000000000 +0200
> @@ -372,8 +372,8 @@ static int slow_work_thread(void *_data)
>  		vsmax *= atomic_read(&slow_work_thread_count);
>  		vsmax /= 100;
>  
> -		prepare_to_wait(&slow_work_thread_wq, &wait,
> -				TASK_INTERRUPTIBLE);
> +		prepare_to_wait_exclusive(&slow_work_thread_wq, &wait,
> +						TASK_INTERRUPTIBLE);
>  		if (!freezing(current) &&
>  		    !slow_work_threads_should_exit &&
>  		    !slow_work_available(vsmax) &&
> 

Should that really be TASK_INTERRUPTIBLE? I don't see anything obvious
in the enclosing for(;;) loop that checks for or handles signals...

Cheers
  Trond
-- 
Trond Myklebust
Linux NFS client maintainer

NetApp
Trond.Myklebust@netapp.com
www.netapp.com