Re: [PATCH] loop.c forgot a kmap

[Andrew Morton <akpm@zip.com.au>]

Benjamin LaHaise wrote:
> 
> The patch below fixes a bug in loop.c that causes highmem systems
> to fail spectacularly when a page happens to be allocated in highmem
> by replacing the use of page_address with a kmap/kunmap sequence.

You must be using a funny kernel, or you have loop on a funny address_space.

The current ->prepare_write() API definition requires that the page be kmapped.
By ->prepare_write.  So it appears that the real bug is actually in whatever
you've mounted your loop on.

Now, Linus (I think) decided that this wasn't a good API and moves were made
to change it.  Note how generic_file_write() kmaps the page as well.  So
we're currently kmapping pages twice on such rare operations as writing
to an ext2 file ;)

So right now, it's unclear whether the kmap should be done by prepare/commit,
or whether it should be done by the caller.  I started to clean it up. Al
disagreed with Linus.  I went and did something else.


-