linux-kernel - Re: [00/17] Large Blocksize Support V3

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Date:	Wed, 25 Apr 2007 08:36:07 -0700 (PDT)
From:	Christoph Lameter <clameter@....com>
To:	Jens Axboe <jens.axboe@...cle.com>
cc:	linux-kernel@...r.kernel.org, Mel Gorman <mel@...net.ie>,
	William Lee Irwin III <wli@...omorphy.com>,
	David Chinner <dgc@....com>,
	Badari Pulavarty <pbadari@...il.com>,
	Maxim Levitsky <maximlevitsky@...il.com>
Subject: Re: [00/17] Large Blocksize Support V3

On Wed, 25 Apr 2007, Jens Axboe wrote:

> I need this patch to actually boot the thing, or it bombs with a NULL
> deref in page_cache_size().

Yeah on 32 bit which I disabled....

> It then boots, doing a little test with 8kb ext2 quickly dies though:
> 
> BUG: unable to handle kernel NULL pointer dereference at virtual address

> EIP: [<d8149519>] 0xd8149519 SS:ESP 0068:e9049d1c
> 
> That's here:
> 
>         page = get_page_from_freelist(gfp_mask|__GFP_HARDWALL, order,
>                                 zonelist, ALLOC_WMARK_LOW|ALLOC_CPUSET);
> ->     if (page)
>                 goto got_pg;

Impossible. page is not dereferenced. Cannot cause a NULL pointer 
deference.

> which doesn't look healthy. Note that this is a 32-bit machine, I
> removed the 32-bit check (devices in this box are fine).


> 
> --- fs/libfs.c~	2007-04-25 13:30:50.000000000 +0200
> +++ fs/libfs.c	2007-04-25 13:31:00.000000000 +0200
> @@ -330,7 +330,7 @@
>  int simple_prepare_write(struct file *file, struct page *page,
>  			unsigned from, unsigned to)
>  {
> -	unsigned int page_size = page_cache_size(file->f_mapping);
> +	unsigned int page_size = page_cache_size(page->mapping);

We do a write operation on a file that has no mapping (and thus no radix 
tree etc etc)? Is that legit?
-
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