[Devel] [PATCH] pfcache: fix path refcounting hazzard

[Konstantin Khorenko]

Andrey, please review the patch.

--
Best regards,

Konstantin Khorenko,
Virtuozzo Linux Kernel Team

On 06/03/2015 08:24 PM, Dmitry Monakhov wrote:
> peer's path management was broken during porting from rhel6 to rhel7
> 
> - open_mapping_peer no longer responsible for path drom on error.
> - fix refcounting during race peer_open/perr_close
> 
> 
> #TESTCASE:
> VEID=101
> mkdir /tmp/pfcache
> mount -ttmpfs none /tmp/pfcache
> vzctl create $VEID
> vzctl mount $VEID
> dd if=/dev/zero of=/vz/root/$VEID/bin/f1 bs=4k count=1
> cp /vz/root/$VEID/bin/f1 /pfcache/1c/eaf73df40e531df3bfb26b4fb7cd95fb7bff1d
> vzctl umount $VEID
> mount /vz/root/$VEID -oremount,balloon_ino=12,pfcache_csum,pfcache=/tmp/pfcache
> stat /vz/root/$VEID/bin/f1 | echo FAIL
> vzctl umount $VEID
> umount /tmp/pfcache || echo FAIL
> 
> Signed-off-by: Dmitry Monakhov <dmonakhov at openvz.org>
> ---
>  fs/ext4/pfcache.c |    2 +-
>  mm/memory.c       |    7 +------
>  2 files changed, 2 insertions(+), 7 deletions(-)
> 
> diff --git a/fs/ext4/pfcache.c b/fs/ext4/pfcache.c
> index 2789508..b75c26d 100644
> --- a/fs/ext4/pfcache.c
> +++ b/fs/ext4/pfcache.c
> @@ -77,6 +77,7 @@ int ext4_open_pfcache(struct inode *inode)
>  	ret = open_mapping_peer(inode->i_mapping, &path, &init_cred);
>  	if (!ret)
>  		percpu_counter_inc(&EXT4_SB(inode->i_sb)->s_pfcache_peers);
> +	path_put(&path);
>  	return ret;
>  }
>  
> @@ -193,7 +194,6 @@ int ext4_relink_pfcache(struct super_block *sb, char *new_root, bool new_sb)
>  		}
>  
>  		if (path.mnt) {
> -			path_get(&path);
>  			if (!open_mapping_peer(inode->i_mapping,
>  						&path, &init_cred))
>  				nr_opened++;
> diff --git a/mm/memory.c b/mm/memory.c
> index 5ec71da..a1ec98f 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -4353,7 +4353,6 @@ restart:
>  	if (!peer->i_peer_file) {
>  		file = dentry_open(path, O_RDONLY | O_LARGEFILE, cred);
>  		if (IS_ERR(file)) {
> -			path_put(path);
>  			return PTR_ERR(file);
>  		}
>  
> @@ -4370,8 +4369,6 @@ restart:
>  		}
>  		if (peer->i_peer_file) {
>  			spin_unlock(&inode->i_lock);
> -			*path = file->f_path;
> -			path_get(path);
>  			fput(file);
>  			file = NULL;
>  			goto restart;
> @@ -4397,9 +4394,7 @@ restart:
>  	if (file) {
>  		file_accessed(file);
>  		fput(file);
> -	} else
> -		path_put(path);
> -
> +	}
>  	return 0;
>  }
>  EXPORT_SYMBOL(open_mapping_peer);
>