Re: [Qemu-devel] [PATCH 3/4] virtiofsd: fix lo_destroy() resource leaks

From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
To: Stefan Hajnoczi <stefanha@redhat.com>
Cc: virtio-fs@redhat.com, Liu Bo <bo.liu@linux.alibaba.com>,
	qemu-devel@nongnu.org
Subject: Re: [Qemu-devel] [PATCH 3/4] virtiofsd: fix lo_destroy() resource leaks
Date: Mon, 5 Aug 2019 16:17:08 +0100	[thread overview]
Message-ID: <20190805151708.GN13734@work-vm> (raw)
In-Reply-To: <20190801165409.20121-4-stefanha@redhat.com>

* Stefan Hajnoczi (stefanha@redhat.com) wrote:
> Now that lo_destroy() is serialized we can call unref_inode() so that
> all inode resources are freed.
> 
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

> ---
>  contrib/virtiofsd/passthrough_ll.c | 43 ++++++++++++++----------------
>  1 file changed, 20 insertions(+), 23 deletions(-)
> 
> diff --git a/contrib/virtiofsd/passthrough_ll.c b/contrib/virtiofsd/passthrough_ll.c
> index a81c01d0d1..02a5e97326 100644
> --- a/contrib/virtiofsd/passthrough_ll.c
> +++ b/contrib/virtiofsd/passthrough_ll.c
> @@ -1340,28 +1340,6 @@ static void unref_inode(struct lo_data *lo, struct lo_inode *inode, uint64_t n)
>  	}
>  }
>  
> -static int unref_all_inodes_cb(gpointer key, gpointer value,
> -			       gpointer user_data)
> -{
> -	struct lo_inode *inode  = value;
> -	struct lo_data *lo = user_data;
> -
> -	inode->nlookup = 0;
> -	lo_map_remove(&lo->ino_map, inode->fuse_ino);
> -	close(inode->fd);
> -	lo_inode_put(lo, &inode); /* Drop our refcount from lo_do_lookup() */
> -
> -	return TRUE;
> -}
> -
> -static void unref_all_inodes(struct lo_data *lo)
> -{
> -	pthread_mutex_lock(&lo->mutex);
> -	g_hash_table_foreach_remove(lo->inodes, unref_all_inodes_cb, lo);
> -	pthread_mutex_unlock(&lo->mutex);
> -
> -}
> -
>  static void lo_forget_one(fuse_req_t req, fuse_ino_t ino, uint64_t nlookup)
>  {
>  	struct lo_data *lo = lo_data(req);
> @@ -2462,6 +2440,18 @@ static void lo_removemapping(fuse_req_t req, struct fuse_session *se,
>  	fuse_reply_err(req, ret);
>  }
>  
> +static int destroy_inode_cb(gpointer key, gpointer value, gpointer user_data)
> +{
> +        struct lo_inode *inode = value;
> +        struct lo_data *lo = user_data;
> +
> +        /* inode->nlookup is normally protected by lo->mutex but see the
> +         * comment in lo_destroy().
> +         */
> +        unref_inode(lo, inode, inode->nlookup);
> +        return TRUE;
> +}
> +
>  static void lo_destroy(void *userdata, struct fuse_session *se)
>  {
>  	struct lo_data *lo = (struct lo_data*) userdata;
> @@ -2475,7 +2465,14 @@ static void lo_destroy(void *userdata, struct fuse_session *se)
>                          fuse_err("%s: unmap during destroy failed\n", __func__);
>                  }
>          }
> -	unref_all_inodes(lo);
> +
> +        /* Normally lo->mutex must be taken when traversing lo->inodes but
> +         * lo_destroy() is a serialized request so no races are possible here.
> +         *
> +         * In addition, we cannot acquire lo->mutex since destroy_inode_cb() takes it
> +         * too and this would result in a recursive lock.
> +         */
> +        g_hash_table_foreach_remove(lo->inodes, destroy_inode_cb, lo);
>  }
>  
>  static struct fuse_lowlevel_ops lo_oper = {
> -- 
> 2.21.0
> 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK