On Thu 16-04-20 15:01:28, Matthew Wilcox wrote:
> From: "Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx>
>
> If this BUG() ever triggers, we'll have a dead system with no particular
> information. Dumping the page will give us a fighting chance of debugging
> the problem, and I think it's safe for us to just continue if we try
> to clear the writeback bit on a page which already has the writeback
> bit clear.
>
> Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
> ---
> mm/filemap.c | 4 +---
> mm/page-writeback.c | 5 +++++
> 2 files changed, 6 insertions(+), 3 deletions(-)
>
> diff --git a/mm/filemap.c b/mm/filemap.c
> index b7c5d2402370..401b24d980ba 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -1293,9 +1293,7 @@ void end_page_writeback(struct page *page)
> rotate_reclaimable_page(page);
> }
>
> - if (!test_clear_page_writeback(page))
> - BUG();
> -
> + test_clear_page_writeback(page);
> smp_mb__after_atomic();
> wake_up_page(page, PG_writeback);
> }
> diff --git a/mm/page-writeback.c b/mm/page-writeback.c
> index 7326b54ab728..ebaf0d8263a6 100644
> --- a/mm/page-writeback.c
> +++ b/mm/page-writeback.c
> @@ -2718,6 +2718,11 @@ int test_clear_page_writeback(struct page *page)
> struct lruvec *lruvec;
> int ret;
>
> + if (WARN_ON(!PageWriteback(page))) {
> + dump_page(page, "!writeback");
> + return false;
> + }
> +
WARN_ON_ONCE() here perhaps? I don't think dumping more pages will bring
that much value...
Honza
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
