On Mon, Nov 23, 2020 at 8:07 PM Hugh Dickins <hughd@xxxxxxxxxx> wrote:
>
> The problem is that PageWriteback is not accompanied by a page reference
> (as the NOTE at the end of test_clear_page_writeback() acknowledges): as
> soon as TestClearPageWriteback has been done, that page could be removed
> from page cache, freed, and reused for something else by the time that
> wake_up_page() is reached.
Ugh.
Would it be possible to instead just make PageWriteback take the ref?
I don't hate your patch per se, but looking at that long explanation,
and looking at the gyrations end_page_writeback() does, I go "why
don't we do that?"
IOW, why couldn't we just make the __test_set_page_writeback()
increment the page count if the writeback flag wasn't already set, and
then make the end_page_writeback() do a put_page() after it all?
Linus
