Re: vm related lock up in 2.6.15

[Linus Torvalds]

On Mon, 9 Jan 2006, Dave Jones wrote:
>  
> Linus,
>  Turns out this was your BUG_ON(page_count(p) <= page_mapcount(p));
> addition to putpage_test_zero, which I added a few days ago and promptly
> forgot about.
> 
> Triggering this isn't too difficult it seems :-/

Well, as I warned in the message that had the patch, the test _is_ racy. 
The reads of the page counts have no serialization, so if another process 
is changing them, I don't guarantee that the test is correct.

IOW, it was meant as a special case debug test for one particular problem 
where I hoped it would give more information, rather than a real patch.

		Linus
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