linux-kernel - Re: [PATCH] ak: fuse: fix premature writetrhough request for large folio

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Message-ID: <aWdYxTEO29S91qp-@fedora.fritz.box>
Date: Wed, 14 Jan 2026 09:58:22 +0100
From: Horst Birthelmer <horst@...thelmer.de>
To: Jingbo Xu <jefflexu@...ux.alibaba.com>
Cc: miklos@...redi.hu, joannelkoong@...il.com, 
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ak: fuse: fix premature writetrhough request for large
 folio


Hi Jingbo,

On Wed, Jan 14, 2026 at 01:56:15PM +0800, Jingbo Xu wrote:
> When large folio is enabled and the initial folio offset exceeds
> PAGE_SIZE, e.g. the position resides in the second page of a large
> folio, after the folio copying the offset (in the page) won't be updated
> to 0 even though the expected range is successfully copied until the end
> of the folio.  In this case fuse_fill_write_pages() exits prematurelly
> before the request has reached the max_write/max_pages limit.
> 
> Fix this by eliminating page offset entirely and use folio offset
> instead.
> 
> Fixes: d60a6015e1a2 ("fuse: support large folios for writethrough writes")
> Cc: stable@...r.kernel.org
> Signed-off-by: Jingbo Xu <jefflexu@...ux.alibaba.com>
> ---
>  fs/fuse/file.c | 10 ++++------
>  1 file changed, 4 insertions(+), 6 deletions(-)
> 
> diff --git a/fs/fuse/file.c b/fs/fuse/file.c
> index 625d236b881b..6aafb32338b6 100644
> --- a/fs/fuse/file.c
> +++ b/fs/fuse/file.c
> @@ -1272,7 +1272,6 @@ static ssize_t fuse_fill_write_pages(struct fuse_io_args *ia,
>  {
>  	struct fuse_args_pages *ap = &ia->ap;
>  	struct fuse_conn *fc = get_fuse_conn(mapping->host);
> -	unsigned offset = pos & (PAGE_SIZE - 1);
>  	size_t count = 0;
>  	unsigned int num;
>  	int err = 0;
> @@ -1299,7 +1298,7 @@ static ssize_t fuse_fill_write_pages(struct fuse_io_args *ia,
>  		if (mapping_writably_mapped(mapping))
>  			flush_dcache_folio(folio);
>  
> -		folio_offset = ((index - folio->index) << PAGE_SHIFT) + offset;
> +		folio_offset = offset_in_folio(folio, pos);
>  		bytes = min(folio_size(folio) - folio_offset, num);
>  
>  		tmp = copy_folio_from_iter_atomic(folio, folio_offset, bytes, ii);
> @@ -1329,9 +1328,6 @@ static ssize_t fuse_fill_write_pages(struct fuse_io_args *ia,
>  		count += tmp;
>  		pos += tmp;
>  		num -= tmp;
> -		offset += tmp;
> -		if (offset == folio_size(folio))
> -			offset = 0;
>  
>  		/* If we copied full folio, mark it uptodate */
>  		if (tmp == folio_size(folio))
> @@ -1343,7 +1339,9 @@ static ssize_t fuse_fill_write_pages(struct fuse_io_args *ia,
>  			ia->write.folio_locked = true;
>  			break;
>  		}
> -		if (!fc->big_writes || offset != 0)
> +		if (!fc->big_writes)
> +			break;
> +		if (folio_offset + tmp != folio_size(folio))
>  			break;
>  	}
>  
> -- 
> 2.19.1.6.gb485710b
> 
> 


I think this might have been an oversight when moving from pages to folios.

Reviewed-by: Horst Birthelmer <hbirthelmer@....com>