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Date: Mon, 05 Oct 2009 14:30:42 +0800
From: Amerigo Wang <amwang@redhat.com>
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To: David Howells <dhowells@redhat.com>
CC: linux-kernel@vger.kernel.org, Brian Behlendorf <behlendorf1@llnl.gov>,
       Ben Woodard <bwoodard@llnl.gov>, Stable Team <stable@kernel.org>,
       akpm@linux-foundation.org
Subject: Re: [Patch] rwsem: fix rwsem_is_locked() bug
References: <20090930032138.3919.72085.sendpatchset@localhost.localdomain> <9705.1254400470@redhat.com>
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David Howells wrote:
> 
> Your patch would probably be better as:
> 
> -	woken = 0;
> +	woken = ++sem->activity;
> 	while (waiter->flags & RWSEM_WAITING_FOR_READ) {
> 		struct list_head *next = waiter->list.next;
> 
> 		list_del(&waiter->list);
> 		tsk = waiter->task;
> 		smp_mb();
> 		waiter->task = NULL;
> 		wake_up_process(tsk);
> 		put_task_struct(tsk);
> 		woken++;
> 		if (list_empty(&sem->wait_list))
> 			break;
> 		waiter = list_entry(next, struct rwsem_waiter, list);
> 	}
> 
> -	sem->activity += woken;
> +	sem->activity = woken;

FYI, this seems wrong, probably even worse than what it is now.
I tried this change, it breaks portmap.