Re: [patch][rfc] 5/5: core remove PageReserved

William Lee Irwin III
2005-06-24T08:24:32Z

William Lee Irwin III <wli@holomorphy.com> wrote:
>> An answer should be devised for this. My numerous SCSI CD-ROM devices
>> (I have 5 across several different machines of several different arches)
>> are rather unlikely to be happy with /* FIXME: XXX ... as an answer.
[...]
>> Mutatis mutandis for my SCSI tape drive.

On Thu, Jun 23, 2005 at 09:50:11PM -0700, Andrew Morton wrote:
> This scsi code is already rather wrong. There isn't much point in just
> setting PG_dirty and leaving the page marked as clean in the radix tree.
> As it is we'll lose data if the user reads it into a MAP_SHARED memory
> buffer.
> set_page_dirty_lock() should be used here. That can sleep.
> The above two functions are called under write_lock_irqsave() (at least)
> and might be called from irq context (dunno). So we cannot use
> set_page_dirty_lock() and we don't have a ref on the page's inode. We
> could use set_page_dirty() and be racy against page reclaim.
> But to get all this correct (and it's very incorrect now) we'd need to punt
> the page dirtying up to process context, along the lines of
> bio_check_pages_dirty().
> Or, if st_unmap_user_pages() and sgl_unmap_user_pages() are not called from
> irq context then we should arrange for them to be called without locks held
> and use set_page_dirty_lock().

This all sounds very reasonable. I was originally more concerned about
the new FIXME getting introduced but this sounds like a good way to
resolve the preexisting FIXME's surrounding all this.

-- wli