Re: [00/17] Large Blocksize Support V3

Christoph Lameter
2007-04-25T15:36:09Z

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?