linux-kernel - Re: [PATCH v2] Btrfs: add another missing end_page_writeback on submit_extent

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Date:   Fri, 10 Feb 2017 17:02:08 +0100
From:   David Sterba <dsterba@...e.cz>
To:     Takafumi Kubota <takafumi.kubota1012@...ab.ics.keio.ac.jp>
Cc:     linux-btrfs@...r.kernel.org, clm@...com, jbacik@...com,
        dsterba@...e.com, linux-kernel@...r.kernel.org,
        bo.li.liu@...cle.com, naota@...sp.net,
        David Sterba <dsterba@...e.cz>
Subject: Re: [PATCH v2] Btrfs: add another missing end_page_writeback on
 submit_extent_page failure

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@...ab.ics.keio.ac.jp>
> Reviewed-by: Liu Bo <bo.li.liu@...cle.com>
> Cc: David Sterba <dsterba@...e.cz>

Added to 4.11 queue, thanks.