Re: deadlocks caused by ext3/reiser dirty_inode calls during do_mmap_pgoff

[Chris Mason <mason@suse.com>]

On Mon, 2004-06-21 at 20:13, Andrew Morton wrote:

> It's super-improbable because we fault the source page in by hand in
> generic_file_aio_write_nolock() via fault_in_pages_readable().  Of course,
> that prefaulting isn't 100% reliable either, because the VM can come in and
> steal the page (or at least unmap its pte) before we get to doing the copy.
> 
> I think we can fix both problems by changing filemap_copy_from_user() and
> filemap_copy_from_user_iovec() to not fall back to kmap() - just fail the
> copy in some way if the atomic copy failed.  Then, in
> generic_file_aio_write_nolock(), do a zero-length ->commit_write(),
> put_page(), then go back and retry the whole thing, starting with
> fault_in_pages_readable().

Oh, just realized this will break our data=ordered setup.  prepare_write
is going to do things like allocating blocks in the file etc etc.  If we
close the transaction via commit_write(0 size) and crash, we'll leak.

We might need to do prefault + pin on the user pages.

-chris