Re: [PATCH 4/4] ipvs: reduce kernel stack usage

[Julian Anastasov]

	Hello,

On Fri, 28 Jun 2019, Arnd Bergmann wrote:

> With the new CONFIG_GCC_PLUGIN_STRUCTLEAK_BYREF_ALL option, the stack
> usage in the ipvs debug output grows because each instance of
> IP_VS_DBG_BUF() now has its own buffer of 160 bytes that add up
> rather than reusing the stack slots:
> 
> net/netfilter/ipvs/ip_vs_core.c: In function 'ip_vs_sched_persist':
> net/netfilter/ipvs/ip_vs_core.c:427:1: error: the frame size of 1052 bytes is larger than 1024 bytes [-Werror=frame-larger-than=]
> net/netfilter/ipvs/ip_vs_core.c: In function 'ip_vs_new_conn_out':
> net/netfilter/ipvs/ip_vs_core.c:1231:1: error: the frame size of 1048 bytes is larger than 1024 bytes [-Werror=frame-larger-than=]
> net/netfilter/ipvs/ip_vs_ftp.c: In function 'ip_vs_ftp_out':
> net/netfilter/ipvs/ip_vs_ftp.c:397:1: error: the frame size of 1104 bytes is larger than 1024 bytes [-Werror=frame-larger-than=]
> net/netfilter/ipvs/ip_vs_ftp.c: In function 'ip_vs_ftp_in':
> net/netfilter/ipvs/ip_vs_ftp.c:555:1: error: the frame size of 1200 bytes is larger than 1024 bytes [-Werror=frame-larger-than=]
> 
> Since printk() already has a way to print IPv4/IPv6 addresses using
> the %pIS format string, use that instead, combined with a macro that
> creates a local sockaddr structure on the stack. These will still
> add up, but the stack frames are now under 200 bytes.
> 
> Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
> ---
> I'm not sure this actually does what I think it does. Someone
> needs to verify that we correctly print the addresses here.
> I've also only added three files that caused the warning messages
> to be reported. There are still a lot of other instances of
> IP_VS_DBG_BUF() that could be converted the same way after the
> basic idea is confirmed.
> ---
>  include/net/ip_vs.h             | 71 +++++++++++++++++++--------------
>  net/netfilter/ipvs/ip_vs_core.c | 44 ++++++++++----------
>  net/netfilter/ipvs/ip_vs_ftp.c  | 20 +++++-----
>  3 files changed, 72 insertions(+), 63 deletions(-)
> 
> diff --git a/include/net/ip_vs.h b/include/net/ip_vs.h
> index 3759167f91f5..3dfbeef67be6 100644
> --- a/include/net/ip_vs.h
> +++ b/include/net/ip_vs.h
> @@ -227,6 +227,16 @@ static inline const char *ip_vs_dbg_addr(int af, char *buf, size_t buf_len,
>  		       sizeof(ip_vs_dbg_buf), addr,			\
>  		       &ip_vs_dbg_idx)
>  
> +#define IP_VS_DBG_SOCKADDR4(fam, addr, port)				\
> +	(struct sockaddr*)&(struct sockaddr_in)				\
> +	{ .sin_family = (fam), .sin_addr = (addr)->in, .sin_port = (port) }
> +#define IP_VS_DBG_SOCKADDR6(fam, addr, port)				\
> +	(struct sockaddr*)&(struct sockaddr_in6) \
> +	{ .sin6_family = (fam), .sin6_addr = (addr)->in6, .sin6_port = (port) }
> +#define IP_VS_DBG_SOCKADDR(fam, addr, port) (fam == AF_INET ?		\
> +			IP_VS_DBG_SOCKADDR4(fam, addr, port) :		\
> +			IP_VS_DBG_SOCKADDR6(fam, addr, port))
> +
>  #define IP_VS_DBG(level, msg, ...)					\
>  	do {								\
>  		if (level <= ip_vs_get_debug_level())			\
> @@ -251,6 +261,7 @@ static inline const char *ip_vs_dbg_addr(int af, char *buf, size_t buf_len,
>  #else	/* NO DEBUGGING at ALL */
>  #define IP_VS_DBG_BUF(level, msg...)  do {} while (0)
>  #define IP_VS_ERR_BUF(msg...)  do {} while (0)
> +#define IP_VS_DBG_SOCKADDR(fam, addr, port) NULL
>  #define IP_VS_DBG(level, msg...)  do {} while (0)
>  #define IP_VS_DBG_RL(msg...)  do {} while (0)
>  #define IP_VS_DBG_PKT(level, af, pp, skb, ofs, msg)	do {} while (0)
> @@ -1244,31 +1255,31 @@ static inline void ip_vs_control_del(struct ip_vs_conn *cp)
>  {
>  	struct ip_vs_conn *ctl_cp = cp->control;
>  	if (!ctl_cp) {
> -		IP_VS_ERR_BUF("request control DEL for uncontrolled: "
> -			      "%s:%d to %s:%d\n",
> -			      IP_VS_DBG_ADDR(cp->af, &cp->caddr),
> -			      ntohs(cp->cport),
> -			      IP_VS_DBG_ADDR(cp->af, &cp->vaddr),
> -			      ntohs(cp->vport));
> +		pr_err("request control DEL for uncontrolled: "
> +		       "%pISp to %pISp\n",

	ip_vs_dbg_addr() used compact form (%pI6c), so it would be
better to use %pISc and %pISpc everywhere in IPVS...

	Also, note that before now port was printed with %d and
ntohs() was used, now port should be in network order, so:

- ntohs() should be removed
- htons() should be added, if missing. At first look, this case
is not present in IPVS, we have only ntohs() usage

Regards

--
Julian Anastasov <ja@xxxxxx>