[lxc-devel] [PATCH] fix multithreaded create()

[Serge Hallyn]

Quoting Dwight Engen (dwight.engen at oracle.com):
> We were calling save_config() twice within the create() flow, each
> from a different process. Depending on order of scheduling, sometimes
> the data from the first save_config() (which was just the stuff from
> LXC_DEFAULT_CONFIG) would overwrite the config we wanted (the full
> config), causing a truncated config file which would then cause lxc
> to segfault once it read it back in because no rootfs.path was set.
> 
> This fixes it by only calling save_config() once in the create()
> flow. A rejected alternative was to call fsync(fileno(fout)) before
> the fclose in save_config.
> 
> Signed-off-by: Dwight Engen <dwight.engen at oracle.com>

Acked-by: Serge E. Hallyn <serge.hallyn at ubuntu.com>

> ---
>  src/lxc/lxccontainer.c | 20 ++++++++++++--------
>  1 file changed, 12 insertions(+), 8 deletions(-)
> 
> diff --git a/src/lxc/lxccontainer.c b/src/lxc/lxccontainer.c
> index c7b2f5e..05ca643 100644
> --- a/src/lxc/lxccontainer.c
> +++ b/src/lxc/lxccontainer.c
> @@ -1192,16 +1192,19 @@ static bool lxcapi_create(struct lxc_container *c, const char *t,
>  	if (lxcapi_is_defined(c) && c->lxc_conf && c->lxc_conf->rootfs.path &&
>  			access(c->lxc_conf->rootfs.path, F_OK) == 0 && tpath) {
>  		ERROR("Container %s:%s already exists", c->config_path, c->name);
> -		free(tpath);
> -		return false;
> +		goto free_tpath;
>  	}
>  
> -	/* Save the loaded configuration to disk */
> -	if (!c->save_config(c, NULL)) {
> -		ERROR("failed to save starting configuration for %s\n", c->name);
> -		goto out;
> +	if (!c->lxc_conf) {
> +		if (!c->load_config(c, LXC_DEFAULT_CONFIG)) {
> +			ERROR("Error loading default configuration file %s\n", LXC_DEFAULT_CONFIG);
> +			goto free_tpath;
> +		}
>  	}
>  
> +	if (!create_container_dir(c))
> +		goto free_tpath;
> +
>  	/*
>  	 * either template or rootfs.path should be set.
>  	 * if both template and rootfs.path are set, template is setup as rootfs.path.
> @@ -1290,10 +1293,11 @@ out_unlock:
>  	if (partial_fd >= 0)
>  		remove_partial(c, partial_fd);
>  out:
> -	if (tpath)
> -		free(tpath);
>  	if (!ret && c)
>  		lxcapi_destroy(c);
> +free_tpath:
> +	if (tpath)
> +		free(tpath);
>  	return ret;
>  }
>  
> -- 
> 1.8.3.1
> 
> 
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