On Fri, Dec 16, 2016 at 03:41:50PM +0900, Takafumi Kubota wrote:
> This is actually inspired by Filipe's patch(55e3bd2e0c2e1).
>
> When submit_extent_page() in __extent_writepage_io() fails,
> Btrfs misses clearing a writeback bit of the failed page.
> This causes the false under-writeback page.
> Then, another sync task hangs in filemap_fdatawait_range(),
> because it waits the false under-writeback page.
>
> CPU0 CPU1
>
> __extent_writepage_io()
> ret = submit_extent_page() // fail
>
> if (ret)
> SetPageError(page)
> // miss clearing the writeback bit
>
> sync()
> ...
> filemap_fdatawait_range()
> wait_on_page_writeback(page);
> // wait the false under-writeback page
>
> Signed-off-by: Takafumi Kubota <takafumi.kubota1...@sslab.ics.keio.ac.jp>
> ---
> fs/btrfs/extent_io.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
> index 1e67723..ef9793b 100644
> --- a/fs/btrfs/extent_io.c
> +++ b/fs/btrfs/extent_io.c
> @@ -3443,8 +3443,10 @@ static noinline_for_stack int
> __extent_writepage_io(struct inode *inode,
> bdev, &epd->bio, max_nr,
> end_bio_extent_writepage,
> 0, 0, 0, false);
> - if (ret)
> + if (ret) {
> SetPageError(page);
> + end_page_writeback(page);
> + }
OK...this could be complex as we don't know which part in
submit_extent_page gets the error, if the page has been added into bio
and bio_end would call end_page_writepage(page) as well, so whichever
comes later, the BUG() in end_page_writeback() would complain.
Looks like commit 55e3bd2e0c2e1 also has the same problem although I
gave it my reviewed-by.
Thanks,
-liubo
>
> cur = cur + iosize;
> pg_offset += iosize;
> --
> 1.9.3
>
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