Subject: Re: [PATCH] hostfs: Fix writeback of dirty pages
To:     Sjoerd Simons <sjoerd@collabora.com>, linux-um@lists.infradead.org
Cc:     Anton Ivanov <anton.ivanov@cambridgegreys.com>,
        Jeff Dike <jdike@addtoit.com>,
        Richard Weinberger <richard@nod.at>,
        linux-kernel@vger.kernel.org, stable@vger.kernel.org
References: <20211105081052.2353801-1-sjoerd@collabora.com>
From:   Christopher Obbard <chris.obbard@collabora.com>
Message-ID: <d9bcb237-39e1-29b1-9718-b720a7e7540b@collabora.com>
Date:   Thu, 11 Nov 2021 13:26:17 +0000
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Hi Sjoerd,

On 05/11/2021 08:10, Sjoerd Simons wrote:
> Hostfs was not setting up the backing device information, which means it
> uses the noop bdi. The noop bdi does not have the writeback capability
> enabled, which in turns means  dirty pages never got written back to
> storage.
> 
> In other words programs using mmap to write to files on  hostfs never
> actually got their data written out...
> 
> Fix this by simply setting up the bdi with default settings as all the
> required code for writeback is already in place.
> 
> Signed-off-by: Sjoerd Simons <sjoerd@collabora.com>

Cc: stable@vger.kernel.org
Reviewed-by: Christopher Obbard <chris.obbard@collabora.com>

...replying mainly as I wonder if adding the stable tag in a reply will 
make the patch appear in stable (obviously once it is in mainline) ? :-)


> 
> ---
> 
>   fs/hostfs/hostfs_kern.c | 3 +++
>   1 file changed, 3 insertions(+)
> 
> diff --git a/fs/hostfs/hostfs_kern.c b/fs/hostfs/hostfs_kern.c
> index d5c9d886cd9f..ef481c3d9019 100644
> --- a/fs/hostfs/hostfs_kern.c
> +++ b/fs/hostfs/hostfs_kern.c
> @@ -924,6 +924,9 @@ static int hostfs_fill_sb_common(struct super_block *sb, void *d, int silent)
>   	sb->s_op = &hostfs_sbops;
>   	sb->s_d_op = &simple_dentry_operations;
>   	sb->s_maxbytes = MAX_LFS_FILESIZE;
> +	err = super_setup_bdi(sb);
> +	if (err)
> +		goto out;
>   
>   	/* NULL is printed as '(null)' by printf(): avoid that. */
>   	if (req_root == NULL)
>