Re: [PATCH v3 15/15] fuse: remove fc->blkbits workaround for partial writes

["Darrick J. Wong" <djwong@kernel.org>]

On Tue, Sep 16, 2025 at 04:44:25PM -0700, Joanne Koong wrote:
> Now that fuse is integrated with iomap for read/readahead, we can remove
> the workaround that was added in commit bd24d2108e9c ("fuse: fix fuseblk
> i_blkbits for iomap partial writes"), which was previously needed to
> avoid a race condition where an iomap partial write may be overwritten
> by a read if blocksize < PAGE_SIZE. Now that fuse does iomap
> read/readahead, this is protected against since there is granular
> uptodate tracking of blocks, which means this workaround can be removed.
> 
> Signed-off-by: Joanne Koong <joannelkoong@gmail.com>

Oh goody!
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>

--D

> ---
>  fs/fuse/dir.c    |  2 +-
>  fs/fuse/fuse_i.h |  8 --------
>  fs/fuse/inode.c  | 13 +------------
>  3 files changed, 2 insertions(+), 21 deletions(-)
> 
> diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c
> index 5c569c3cb53f..ebee7e0b1cd3 100644
> --- a/fs/fuse/dir.c
> +++ b/fs/fuse/dir.c
> @@ -1199,7 +1199,7 @@ static void fuse_fillattr(struct mnt_idmap *idmap, struct inode *inode,
>  	if (attr->blksize != 0)
>  		blkbits = ilog2(attr->blksize);
>  	else
> -		blkbits = fc->blkbits;
> +		blkbits = inode->i_sb->s_blocksize_bits;
>  
>  	stat->blksize = 1 << blkbits;
>  }
> diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
> index cc428d04be3e..1647eb7ca6fa 100644
> --- a/fs/fuse/fuse_i.h
> +++ b/fs/fuse/fuse_i.h
> @@ -975,14 +975,6 @@ struct fuse_conn {
>  		/* Request timeout (in jiffies). 0 = no timeout */
>  		unsigned int req_timeout;
>  	} timeout;
> -
> -	/*
> -	 * This is a workaround until fuse uses iomap for reads.
> -	 * For fuseblk servers, this represents the blocksize passed in at
> -	 * mount time and for regular fuse servers, this is equivalent to
> -	 * inode->i_blkbits.
> -	 */
> -	u8 blkbits;
>  };
>  
>  /*
> diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
> index fdecd5a90dee..5899a47faaef 100644
> --- a/fs/fuse/inode.c
> +++ b/fs/fuse/inode.c
> @@ -292,7 +292,7 @@ void fuse_change_attributes_common(struct inode *inode, struct fuse_attr *attr,
>  	if (attr->blksize)
>  		fi->cached_i_blkbits = ilog2(attr->blksize);
>  	else
> -		fi->cached_i_blkbits = fc->blkbits;
> +		fi->cached_i_blkbits = inode->i_sb->s_blocksize_bits;
>  
>  	/*
>  	 * Don't set the sticky bit in i_mode, unless we want the VFS
> @@ -1810,21 +1810,10 @@ int fuse_fill_super_common(struct super_block *sb, struct fuse_fs_context *ctx)
>  		err = -EINVAL;
>  		if (!sb_set_blocksize(sb, ctx->blksize))
>  			goto err;
> -		/*
> -		 * This is a workaround until fuse hooks into iomap for reads.
> -		 * Use PAGE_SIZE for the blocksize else if the writeback cache
> -		 * is enabled, buffered writes go through iomap and a read may
> -		 * overwrite partially written data if blocksize < PAGE_SIZE
> -		 */
> -		fc->blkbits = sb->s_blocksize_bits;
> -		if (ctx->blksize != PAGE_SIZE &&
> -		    !sb_set_blocksize(sb, PAGE_SIZE))
> -			goto err;
>  #endif
>  	} else {
>  		sb->s_blocksize = PAGE_SIZE;
>  		sb->s_blocksize_bits = PAGE_SHIFT;
> -		fc->blkbits = sb->s_blocksize_bits;
>  	}
>  
>  	sb->s_subtype = ctx->subtype;
> -- 
> 2.47.3
> 
>