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Date:   Thu, 13 Feb 2020 22:01:09 +0100
From:   David Sterba <dsterba@suse.cz>
To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc:     linux-kernel@vger.kernel.org, stable@vger.kernel.org,
        Filipe Manana <fdmanana@suse.com>,
        Josef Bacik <josef@toxicpanda.com>,
        David Sterba <dsterba@suse.com>,
        Sasha Levin <sashal@kernel.org>
Subject: Re: [PATCH 4.9 089/116] btrfs: flush write bio if we loop in
 extent_write_cache_pages
Message-ID: <20200213210109.GS2902@suse.cz>
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        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        linux-kernel@vger.kernel.org, stable@vger.kernel.org,
        Filipe Manana <fdmanana@suse.com>,
        Josef Bacik <josef@toxicpanda.com>, David Sterba <dsterba@suse.com>,
        Sasha Levin <sashal@kernel.org>
References: <20200213151842.259660170@linuxfoundation.org>
 <20200213151917.511897953@linuxfoundation.org>
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On Thu, Feb 13, 2020 at 07:20:33AM -0800, Greg Kroah-Hartman wrote:
> From: Josef Bacik <josef@toxicpanda.com>
> 
> [ Upstream commit 96bf313ecb33567af4cb53928b0c951254a02759 ]

This commit does not exist in my tree, the correct upstream commit of
the backported patch should be 42ffb0bf584ae5b6b38f72259af1e0ee417ac77f.

> --- a/fs/btrfs/extent_io.c
> +++ b/fs/btrfs/extent_io.c
> @@ -4060,6 +4060,14 @@ static int extent_write_cache_pages(struct extent_io_tree *tree,
>  		 */
>  		scanned = 1;
>  		index = 0;
> +
> +		/*
> +		 * If we're looping we could run into a page that is locked by a
> +		 * writer and that writer could be waiting on writeback for a
> +		 * page in our current bio, and thus deadlock, so flush the
> +		 * write bio here.
> +		 */
> +		flush_write_bio(data);

This has been modified to apply, flush_write_bio does not return a value
in 4.9, perhaps this led to the different commit id.