linux-kernel - Re: __getblk infinite loop

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Date:	Fri, 5 Sep 2008 10:58:55 -0400
From:	"Bob Copeland" <me@...copeland.com>
To:	"Andrew Morton" <akpm@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org, snakebyte@....de
Subject: Re: __getblk infinite loop

On Fri, Sep 5, 2008 at 1:38 AM, Andrew Morton <akpm@...ux-foundation.org> wrote:
> That loop does lock up on people occasionally - last time was in isofs,
> because it had done an insane set_blocksize() earlier on.
>
> Yes, it's always a case of garbage in, garbage out (or nothing out, as
> the case may be).
>
> No, it's not particularly programmer-friendly behaviour.

Ok, I think I get it now - sector_t 0x1d4000004 is in the addressable
range (by one bit) since we can address 4G blocks of PAGE_SIZE and the
FS is using a block size of 2048.  grow_buffers() always returns 0
because find_or_create_page() fails adding a page with that huge
offset into the pagecache (?), so we try to free memory and try again.
 Your patch here:

    http://marc.info/?l=linux-kernel&m=117202372525279&w=2

doesn't apply to the situation since index is still technically a
valid page offset.

So, I guess the answer is to deal with it in fsck and tell people
"don't do that."
-- 
Bob Copeland %% www.bobcopeland.com
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