Re: [PATCH v2 hulk-4.1-next 2/7] 9p: ->evict_inode() should kick out ->i_data, not, ->i_mapping

[jiangyiwen <jiangyiwen@huawei.com>]

On 2018/1/19 11:46, jiangyiwen wrote:
> mainline inclusion
> from v4.4-rc5
> commit 4ad78628445d26e5e9487b2e8f23274ad7b0f5d3
> category: bugfix
> bugzilla: 4404
> DTS: NA
> CVE: NA
> 补丁作用：对于块设备文件而言，->i_mapping与
> 普通文件不相同，如果文件中的数据来自于块设备
> 文件，则其->i_mapping将指向的是bdevfs inode
> （master inode）的i_data，而->i_data实际是
> empty的，因此在evict_inode的时候不应该释放
> ->i_mapping（bdevfs_inode->i_data）的所有
> pagecache；同时->i_mapping只有在文件被打开
> 的时候才能访问，此时已经是文件被关闭时不应
> 该访问该变量。
> 
> -------------------
> [ Upstream commit 4ad78628445d26e5e9487b2e8f23274ad7b0f5d3 ]
> 
> For block devices the pagecache is associated with the inode
> on bdevfs, not with the aliasing ones on the mountable filesystems.
> The latter have its own ->i_data empty and ->i_mapping pointing
> to the (unique per major/minor) bdevfs inode.  That guarantees
> cache coherence between all block device inodes with the same
> device number.
> 
> Eviction of an alias inode has no business trying to evict the
> pages belonging to bdevfs one; moreover, ->i_mapping is only
> safe to access when the thing is opened.  At the time of
> ->evict_inode() the victim is definitely *not* opened.  We are
> about to kill the address space embedded into struct inode
> (inode->i_data) and that's what we need to empty of any pages.
> 
> 9p instance tries to empty inode->i_mapping instead, which is
> both unsafe and bogus - if we have several device nodes with
> the same device number in different places, closing one of them
> should not try to empty the (shared) page cache.
> 
> Fortunately, other instances in the tree are OK; they are
> evicting from &inode->i_data instead, as 9p one should.
> 
> Cc: stable@vger.kernel.org # v2.6.32+, ones prior to 2.6.36 need only half of that
> Reported-by: "Suzuki K. Poulose" <Suzuki.Poulose@arm.com>
> Tested-by: "Suzuki K. Poulose" <Suzuki.Poulose@arm.com>
> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
> Signed-off-by: Yiwen Jiang <jiangyiwen@huawei.com>
> ---
>  fs/9p/vfs_inode.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/9p/vfs_inode.c b/fs/9p/vfs_inode.c
> index 3d1f365..9b96add 100644
> --- a/fs/9p/vfs_inode.c
> +++ b/fs/9p/vfs_inode.c
> @@ -451,9 +451,9 @@ void v9fs_evict_inode(struct inode *inode)
>  {
>  	struct v9fs_inode *v9inode = V9FS_I(inode);
> 
> -	truncate_inode_pages_final(inode->i_mapping);
> +	truncate_inode_pages_final(&inode->i_data);
>  	clear_inode(inode);
> -	filemap_fdatawrite(inode->i_mapping);
> +	filemap_fdatawrite(&inode->i_data);
> 
>  	v9fs_cache_inode_put_cookie(inode);
>  	/* clunk the fid stashed in writeback_fid */
> 
Hi all,

Sorry, It's my fault, please ignore this email.

Thanks,
Yiwen.