On Thu, 11 Nov 2010 11:05:54 +0800 Bob Liu <lliubbo@xxxxxxxxx> wrote:
> __set_page_dirty_no_writeback() should return true if it actually transitioned
> the page from a clean to dirty state although it seems nobody used its return
> value now.
>
> Change from v1:
> * preserving cacheline optimisation as Andrew pointed out
>
> Signed-off-by: Bob Liu <lliubbo@xxxxxxxxx>
> ---
> mm/page-writeback.c | 4 +++-
> 1 files changed, 3 insertions(+), 1 deletions(-)
>
> diff --git a/mm/page-writeback.c b/mm/page-writeback.c
> index bf85062..ac7018a 100644
> --- a/mm/page-writeback.c
> +++ b/mm/page-writeback.c
> @@ -1157,8 +1157,10 @@ EXPORT_SYMBOL(write_one_page);
> */
> int __set_page_dirty_no_writeback(struct page *page)
> {
> - if (!PageDirty(page))
> + if (!PageDirty(page)) {
> SetPageDirty(page);
> + return 1;
> + }
> return 0;
> }
But that has a race. If someone else sets PG_Dirty between the test
and the set, this function will incorrectly return 1.
Which is why it should use test_and_set if we're going to do this.
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