linux-kernel - Re: [Patch] rwsem: fix rwsem_is

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Message-ID: <4AC99292.5060502@redhat.com>
Date:	Mon, 05 Oct 2009 14:30:42 +0800
From:	Amerigo Wang <amwang@...hat.com>
To:	David Howells <dhowells@...hat.com>
CC:	linux-kernel@...r.kernel.org,
	Brian Behlendorf <behlendorf1@...l.gov>,
	Ben Woodard <bwoodard@...l.gov>,
	Stable Team <stable@...nel.org>, akpm@...ux-foundation.org
Subject: Re: [Patch] rwsem: fix rwsem_is_locked() bug

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.

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