linux-kernel - Re: [PATCH] mm: fix possible cause of a page

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Message-ID: <AANLkTi==MQV=_qq1HaCxGLRu8DdT6FYddqzBkzp1TQs7@mail.gmail.com>
Date:	Mon, 28 Feb 2011 15:35:40 -0800
From:	Robert Święcki <robert@...ecki.net>
To:	Hugh Dickins <hughd@...gle.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Miklos Szeredi <miklos@...redi.hu>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH] mm: fix possible cause of a page_mapped BUG

> But rather than exporting the notion of restart_addr from memory.c, or
> converting to restart_pgoff throughout, simply reset vm_truncate_count
> to 0 to force a rescan if mremap move races with preempted truncation.
>
> We have no confirmation that this fixes Robert's BUG,
> but it is a fix that's worth making anyway.

Hi, I don't have currently access to my rs232/console testing machine
(lame excuse but it helps a lot;), cause I'm working currently OOtO,
so I'll try to test it asap - which is probably Mar 15th or so.

Btw, the fuzzer is here: http://code.google.com/p/iknowthis/

I think i was trying it with this revision:
http://code.google.com/p/iknowthis/source/detail?r=11 (i386 mode,
newest 'iknowthis' supports x86-64 natively), so feel free to try it.

It used to crash the machine (it's BUG_ON but the system became
unusable) in matter of hours. Btw, when I was testing it for the last
time it Ooopsed much more frequently in proc_readdir (I sent report in
one of earliet e-mails).

> Signed-off-by: Hugh Dickins <hughd@...gle.com>
> ---
>
>  mm/mremap.c |    4 +---
>  1 file changed, 1 insertion(+), 3 deletions(-)
>
> --- 2.6.38-rc6/mm/mremap.c      2011-01-18 22:04:56.000000000 -0800
> +++ linux/mm/mremap.c   2011-02-23 15:29:52.000000000 -0800
> @@ -94,9 +94,7 @@ static void move_ptes(struct vm_area_str
>                 */
>                mapping = vma->vm_file->f_mapping;
>                spin_lock(&mapping->i_mmap_lock);
> -               if (new_vma->vm_truncate_count &&
> -                   new_vma->vm_truncate_count != vma->vm_truncate_count)
> -                       new_vma->vm_truncate_count = 0;
> +               new_vma->vm_truncate_count = 0;
>        }
>
>        /*
>



-- 
Robert Święcki
--
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