Re: [PATCH v2] Btrfs: add another missing end_page_writeback on submit_extent_page failure

[David Sterba]

On Thu, Feb 09, 2017 at 05:24:33PM +0900, Takafumi Kubota wrote:
> If btrfs_bio_alloc fails in submit_extent_page, submit_extent_page returns
> without clearing the writeback bit of the failed page.
> 
> __extent_writepage_io, that is a caller of submit_extent_page,
> does not clear the remaining writeback bit anywhere.
> As a result, this will cause the hang at filemap_fdatawait_range,
> because it waits the writeback bit to be cleared from the failed page.
> So, we have to call end_page_writeback to clear the writeback bit.
> 
> For reproducing the hang, we inject a fault like
> 
>    if (should_failtest()) { // I define should_failtest()
>         bio = NULL;
>    }
>    else {
>         bio = btrfs_bio_alloc(...);
>    }
> 
> in submit_extent_page.
> 
> We should also check whether page has the bit before end_page_writeback,
> to avoid the conflict against the other end_page_writeback in bio_endio.
> Thus, we add PageWriteback checks not only in __extent_writepage_io,
> but also in write_one_eb too, because it misses the check.
> 
> Signed-off-by: Takafumi Kubota <takafumi.kubota1012@xxxxxxxxxxxxxxxxxxxx>
> Reviewed-by: Liu Bo <bo.li.liu@xxxxxxxxxx>
> Cc: David Sterba <dsterba@xxxxxxx>

Added to 4.11 queue, thanks.