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

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Message-ID: <CAK8P3a0xPDmNDbxRkN6ssobFLu1-JLvMG3MSai844hinj2Bs8A@mail.gmail.com>
Date:   Mon, 22 Jul 2019 12:28:59 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Willem de Bruijn <willemdebruijn.kernel@...il.com>
Cc:     Kees Cook <keescook@...omium.org>,
        Wensong Zhang <wensong@...ux-vs.org>,
        Simon Horman <horms@...ge.net.au>,
        Julian Anastasov <ja@....bg>,
        "David S. Miller" <davem@...emloft.net>,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        Pablo Neira Ayuso <pablo@...filter.org>,
        Jozsef Kadlecsik <kadlec@...filter.org>,
        Florian Westphal <fw@...len.de>,
        James Smart <james.smart@...adcom.com>,
        Dick Kennedy <dick.kennedy@...adcom.com>,
        "James E . J . Bottomley" <jejb@...ux.ibm.com>,
        "Martin K . Petersen" <martin.petersen@...cle.com>,
        Larry Finger <Larry.Finger@...inger.net>,
        Florian Schilhabel <florian.c.schilhabel@...glemail.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        James Morris <jmorris@...ei.org>,
        linux-scsi <linux-scsi@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        driverdevel <devel@...verdev.osuosl.org>,
        Network Development <netdev@...r.kernel.org>,
        lvs-devel@...r.kernel.org,
        netfilter-devel <netfilter-devel@...r.kernel.org>,
        coreteam@...filter.org, Ard Biesheuvel <ard.biesheuvel@...aro.org>
Subject: Re: [PATCH 4/4] ipvs: reduce kernel stack usage

On Fri, Jun 28, 2019 at 9:59 PM Willem de Bruijn
<willemdebruijn.kernel@...il.com> wrote:
> On Fri, Jun 28, 2019 at 8:40 AM Arnd Bergmann <arnd@...db.de> 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,
>
> since these are sockaddr_in and sockaddr_in6, should that have the 'n'
> specifier to denote network byteorder?

I double-checked the implementation, and don't see that make any difference,
as 'n' is the default.

> >  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) }
>
> might as well set .sin_family = AF_INET here and AF_INET6 below?

That would work just same, but I don't see any advantage. As the family
and port members are the same between sockaddr_in and sockaddr_in6,
the compiler can decide to set these regardless to the argument values
regardless of the condition.

       Arnd