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Date: Tue, 28 Aug 2001 17:27:52 +0100 (BST)
From: Hugh Dickins <hugh@veritas.com>
To: Rik van Riel <riel@conectiva.com.br>
cc: Marcelo Tosatti <marcelo@conectiva.com.br>, Ingo Molnar <mingo@elte.hu>,
        lkml <linux-kernel@vger.kernel.org>
Subject: Re: find_get_swapcache_page() question
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On Tue, 28 Aug 2001, Rik van Riel wrote:
> On Tue, 28 Aug 2001, Hugh Dickins wrote:
> 
> > 		if (!PageSwapCache(found))
> > 			BUG();
> > 		if (found->mapping != &swapper_space)
> > 			BUG();
> > are not safe, since there may a concurrent remove_from_swap_cache(),
> > either from try_to_unuse() or from Rik's new vm_swap_full() deletion.
> > Those tests would be safe if the page were locked, but it's not.
> 
> vm_swap_full() is called with the page locked,
> remove_from_swap_cache() also seems to want the
> page locked...

Certainly (I seem to recall composing a comment to that effect
recently :-)!  Sorry for being unclear, I meant that those tests
in lookup_swap_cache() are made without the page being locked
by lookup_swap_cache() or its caller (and I'm not proposing
that the page should be locked, but the unsafe tests removed).

Hugh